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What Makes Things Float?An Immersion Unit Investigating Density and Buoyancy

June 2006DRAFT 2

8th Grade Physical Science Immersion Unit

Buoyancy and Density:

What Makes Things Float?

This Grade 8 Immersion Unit is being developed in partnership with the Los Angeles Unified School District and is being tested and revised by teachers, scientists, and curriculum developers associated with the NSF-funded Math/Science Partnership, System-wide Change for All Learners and Educators (SCALE) and the DOE-funded Quality Educator Development (QED) project at the California State University–Dominguez Hills.

Immersion Units provide a coherent series of lessons designed to guide students in developing deep conceptual understanding that is aligned with the standards and key concepts in science. In Immersion Units, students learn academic content by working like scientists: making observations, asking questions, doing further investigations to explore and explain natural phenomena, and communi-cating their results based on evidence.

Table of Contents �

Table of ContentsNavigating the Unit ..................................................................................................7

Unit Overview ...........................................................................................................9

Unit Overarching Concepts ........................................................................................9Unit Supporting Concepts ..........................................................................................9Evidence of Student Understanding ..........................................................................9Unit Preview .................................................................................................................9Unit Standards ...........................................................................................................10Unit Timeline..............................................................................................................11Unit Content Background .........................................................................................13Unit Investigation ......................................................................................................13What Makes Things Float? Unit Level Graphic Organizer ..................................13What Makes Things Float? Chart ...........................................................................14Support Materials ......................................................................................................16

Step 1 Overview .....................................................................................................19

Step 1 Lesson 1 Snapshot: Floating Puzzles ............................................................21Teacher Background Information .........................................................................23Implementation Guide ..........................................................................................27Student Page 1.1A: Floating Puzzles ....................................................................29

Step 1 Lesson 2 Snapshot: Crafting Testable Questions ........................................31Teacher Background Information .........................................................................33Implementation Guide ..........................................................................................34Student Page 1.2A: Questions for Investigations ..................................................35Teacher Page 1.2a: Questions for Investigations ..................................................37

Step 2 Overview .....................................................................................................�9Step 2 Lesson 1 Snapshot: Mass and Floating ........................................................41

Teacher Background Information .........................................................................43Advance Preparation .............................................................................................43Implementation Guide ..........................................................................................44Student Page 2.1A: What Makes Things Float? ...................................................47

Step 2 Lesson 2 Snapshot: How Heavy? ..................................................................49Teacher Background Information .........................................................................51Advance Preparation .............................................................................................52Implementation Guide ..........................................................................................53

� Buoyancy and Density: What Makes Things Float?

Step 2 Lesson 3 Snapshot: Analyzing Data to Predict What Will Float ...............55Teacher Background Information .........................................................................57Advance Preparation .............................................................................................57Implementation Guide ..........................................................................................58Student Page 2.3A: Graphing Results ...................................................................61Student Page 2.3B: Interpreting Data ...................................................................63Teacher Page 2.3c: Think Aloud Notes for Analyzing Results .............................65

Step 2 Lesson 4 Snapshot: Density Defined .............................................................67Implementation Guide ..........................................................................................69Student Page 2.4A: What is Density? ...................................................................71

Step 2 Lesson 5 Snapshot: Milestone Challenge #1: Using What We Know about Floating and Sinking .................................................................................................73

Advance Preparation .............................................................................................75Implementation Guide ..........................................................................................76Student Page 2.5A: What Does Density Have To Do With Floating? ..................77Teacher Page 2.5a: What Does Density Have To Do With Floating? ...................79

Step � Overview .....................................................................................................81

Step 3 Lesson 1 Snapshot: Displacement in a Liquid.............................................83Advance Preparation .............................................................................................85Implementation Guide ..........................................................................................86Student Page 3.1A: Displacement in a Liquid ......................................................89Student Page 3.1A: Displacement in a Liquid (continued)...................................91Student Page 3.1A: Displacement in a Liquid (continued)...................................93Teacher Page 3.1a: Displacement in a Liquid .......................................................95

Step 3 Lesson 2 Snapshot: Milestone Challenge #2—Which Medal? ...................97Implementation Guide ..........................................................................................99Student Page 3.2A: Milestone Challenge #2—Which Medal? ...........................101

Step � Overview: Buoyancy and Forces ..............................................................10�

Step 4 Lesson 1 Snapshot: Exploring Apparent Weight and Buoyancy .............105Teacher Background Information .......................................................................107Advance Preparation ...........................................................................................107Implementation Guide ........................................................................................108Student .1A: Drawing Forces ...................................................................111Student Page 4.1A: Drawing Forces (continued)................................................113Student Page 4.1B: Archimedes Investigations ..................................................115Student Page 4.1B: Archimedes Investigations (continued) ...............................117Teacher Page 4.1a: Forces ...................................................................................119

Step 4 Lesson 2 Snapshot: A Balance of Forces ....................................................121Teacher Background Information .......................................................................123Implementation Guide ........................................................................................124Student Page 4.2A: A Balance of Forces ............................................................127Student Page 4.2A: A Balance of Forces (continued) .........................................129

Table of Contents �

Student Page 4.2B: Remembering Archimedes ..................................................131Teacher Page 4.2a: A Balance of Forces .............................................................133

Step 4 Lesson 3 Snapshot: Predicting Payload .....................................................135Teacher Background Information .......................................................................137Advance Preparation ...........................................................................................138Implementation Guide ........................................................................................140Student Page 4.3A: Milestone Challenge #3—Predicting Payload ....................141

Step � Overview: Fluids and Buoyancy ................................................................1��

Step 5 Lesson 1 Snapshot: Liquids and Buoyancy ...............................................145Teacher Background Information .......................................................................147Advance Preparation ...........................................................................................148Implementation Guide ........................................................................................149Student .1A: Liquids and Buoyancy ........................................................151Teacher Page 5.1a: Liquids and Buoyancy .........................................................153Teacher Page 5.1b: Density Table .......................................................................155

Step 5 Lesson 2 Snapshot: Gases and Buoyancy ..................................................157Teacher Background Information .......................................................................159Implementation Guide ........................................................................................160Student Page 5.2A: Gases in the Ocean ..............................................................163Student Page 5.2A: Gases in the Ocean (continued) ..........................................165Teacher Page 5.2a: Gases in the Ocean ..............................................................167Teacher Page 5.2a: Gases in the Ocean (continued) ...........................................169Teacher Page 5.2a: Gases in the Ocean (continued) ...........................................171

Step 6 Overview: Unit Evaluation.........................................................................17�

Step 6 Lesson 1 Snapshot: Density and Buoyancy Misconceptions: Oil Spill ...175Implementation Guide ........................................................................................177Student Page 6.1A: The Exxon Valdez ...............................................................179Student Page 6.1A: The Exxon Valdez (continued) ............................................181

Step 6 Lesson 2 Snapshot: Inquiry into Density and Buoyancy..........................183Student Page 6.2A: Scientific Investigation ........................................................185

6 Buoyancy and Density: What Makes Things Float?

Unit Overview 7

Navigating the Unit

This Immersion Unit provides a coherent series of lessons designed to guide students in developing deep conceptual understanding that is aligned with the standards, key science concepts, and essential features of classroom inquiry (as defined by the National Science Education Standards). In Immersion Units, students learn academic content by working like scientists: making observations, asking questions, doing further investigations to explore and explain natural phenomena, and communicating results based on evidence. Immersion Units are intended to support teachers in building a learning culture in their classrooms to sustain students’ enthusiasm for engaging in scientific habits of thinking while learning rigorous science content.

This Immersion Unit is comprised of several steps; each step contains between one and four lessons. The unit begins with the Unit Overview, which includes a description of the key concepts, evidence for student understanding, assessment strategies and other relevant implementation information. The Unit Overview outlines the conceptual flow and rationale for the structure of the unit.

Each step in the unit begins with an overview, which describes the individual goals and activities of the specific step, and its relationship to the previous and following steps. The title and approximate length of time needed for each lesson is also shown. Within the step, each lesson contains:

• Snapshot • Background Information• Implementation Guide• Student Pages• Teacher Pages

Snapshots are printed on a single page and provide key information for implementing the lesson. Each snapshot includes the key concept(s), evidence of student understanding, list of materials, procedures for lesson implementation, key words and REAPS—a strategy for assessing student learning. This page is designed to have on hand while you implement the lesson.

The Background Information and Implementation Guide sections provide learning experiences such as investigations, reading research, or other engaging supporting strategies designed to teach a specific concept(s). They include instructions for any advance preparation required, explain the design of the lesson, include strategies for assessing student learning, and provide teacher background information on relevant science content. The Implementation Guide for each lesson addresses teaching methodology, including specific examples and information related to effective teacher implementation. If research identifies common misconceptions related to the content, a detailed explanation of common misconceptions is provided with suggestions for addressing them.

Student pages may include readings, guides, handouts, maps or instructions to engage students during the lesson. These pages assist you as you guide students through the lesson, and are intended to be readily adapted to suit a variety of classrooms with diverse student populations.

Teacher pages may include overheads, maps, data charts and other materials that can help you implement the lesson.

Snapshot Page

The information on the Snapshot page includes the following:• Lesson Title • Materials• Key Concept • Key Words• Time Needed • REAPS Questions

(continued on following page)


This Immersion Unit contains a variety of opportunities for modifying content and methodology based on your students’ needs and your classroom situation. The basic structure of the unit is designed to support you in anticipating

the particular needs of your students to foster understanding of inquiry, nurture classroom communities of science learners, and engage students in learning key science concepts.

Unit Overview 9

Unit Overarching Concepts• Density is the relationship between mass

and volume and is an intrinsic property of materials under stable conditions.

• Whether an object will float or sink can be predicted by comparing the object’s density to the density of the fluid in which the object is immersed.

• Science knowledge advances through inquiry.

Unit Supporting Concepts• The density of an object can be calculated

from measurements of mass and volume taken from the object.

• The volume of an irregular solid can be measured using water displacement.

• Equal volumes of different substances usually have different weights.

• Buoyancy is a balance between the gravitational force and buoyant force.

• Scientists differ greatly in what phenomena they study and how they go about their work. Although there is no fixed set of steps that all scientists follow, scientific investigations usually involve the collection of relevant evidence, the use of logical reasoning, and the application of imagination in devising hypotheses and explanations to make sense of the collected evidence (Benchmarks quote).

Evidence of Student UnderstandingBy the end of this unit, the student will be able to:

• demonstrate that density is a physical property of an object and is independent of the amount of substance being examined

• explain graphically and orally that the ratio of an object’s mass to volume is its density

• calculate the density of a an object from measurements of mass and volume taken from the object

• explain that the buoyant force acting on an object that is immersed in a fluid is an upward force equal to the weight of the fluid displaced by the object

• analyze and correct the explanation in a real-life scenario to accurately reflect the scientific understanding that the buoyant force acting on an object opposes the force of gravity acting on the object and the magnitude of the buoyant force depends on the difference between the object’s density and the density of the fluid in which the object is immersed

• use an appropriate combination of evidence to predict whether an object will float or sink by comparing the object’s density to the density of the fluid in which the object is immersed

• identify and engage in all aspects of scientific inquiry.

• explain how studying natural phenomena through scientific inquiry advances knowledge.

• construct appropriate graphs from data and develop qualitative statements about the relationships between variables.

Unit PreviewWhat makes things float? This simple question opens the door to several fundamental concepts in the physical sciences, including how density and a balance of forces determine whether an object will float. These concepts are directly observable and can easily be investigated by 8th grade students.

In this unit, students begin by exploring the overarching question, “What makes things float?” through a series of observations and questions about odd pairs of floating and sinking objects. The unit continues through a series of three steps in which students engage in short investigations to explain the


Unit StandardsDensity and BuoyancyAll objects experience a buoyant force when immersed in a fluid. As a basis for understanding this concept:

a) Students know density is mass per unit volume.b) Students know how to calculate the density of substances (regular and

irregular solids and liquids) from measurements of mass and volume.c) Students know the buoyant force on an object in a fluid is an upward

force equal to the weight of the fluid the object has displaced.d) Students know how to predict whether an object will float or sink.

ForcesUnbalanced forces cause changes in velocity. As a basis for understanding this concept:

a) Students know a force has both direction and magnitude.b) Students know when an object is subject to two or more forces at once,

the result is the cumulative effect of all the forces.c) Students know when the forces on an object are balanced; the motion of

the object does not change.d) Students know that when the forces on an object are unbalanced, the

object will change its velocity (that is, it will speed up, slow down, or change direction).e)

f) Students know the greater the mass of an object, the more force is needed to achieve the same rate of change in motion.

Investigation and ExperimentationScientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students will develop their own questions and perform investigations. Students will:

a) Plan and conduct a scientific investigation to test a hypothesis.b) Evaluate the accuracy and reproducibility of data.c) Distinguish between variable and controlled parameters in a test.d) Recognize the slope of the linear graph as the constant in the relationshipe) y = kx and apply this principle in interpreting graphs constructed from

data.f) Construct appropriate graphs from data and develop quantitative

statements about the relationships between variables.g) Apply simple mathematic relationships to determine a missing quantity

in a mathematic expression, given the two remaining terms (including speed = distance/time, density = mass/volume, force = pressure × area, volume = area × height).

h) Distinguish between linear and nonlinear relationships on a graph of data.

Unit Overview 11

factors that determine whether an object will sink or float. In Step 5, students are introduced to density and buoyancy in liquids and gases and the effect that temperature has on these properties. In the final step, students apply what they have learned about those factors to interpret how density and buoyancy played a role in the oil spill that followed the grounding

Unit Timeline

Step LessonClass Time

Key Concepts

Step 1 Step 1 Lesson 1Floating Puzzles 50 min

• Scientists observe natural phenomena, pose questions, and wonder based on their observations.

Step 1 Lesson 2Crafting Testable

Questions50 min

• Scientists observe natural phenomena and develop testable questions based on their observations.

Step 2 Step 2 Lesson 1Mass and Floating

50 min

• Scientists use precise measurements to make accurate explanations.

• Heavier cubes are more likely to sink than lighter cubes (of equal volume).

Step 2 Lesson 2Floating Data 50 min

• Two different-sized objects made of the same material sink or float the same way.

• Heavy things may float or sink depending on their size.

Step 2 Lesson 3Analyzing Floating

Data 50 min

• Objects with a density less than the density of water (1 g/cm3) will float in water at some level.

• Under stable conditions, the density of a substance is a standard property of that substance and does not change.

Step 2 Lesson 4Defining Density

50 min

• Objects with a density less than the density of water (1 g/cm3) will float in water at some level.


Step 2 Lesson 5Challenge #1 –

Density50 min

• Objects with a density less than the density of water (1g/cm3) will float in water at some level.

of the Exxon Valdez tanker, a widely publicized event from 1989. As students work through the basic principles outlined in the overarching and supporting concepts through direct observation, testing, and measurement, they develop an enduring understanding of density and buoyancy and the ability to apply what they learn to solve problems.


Step LessonClass Time

Key Concepts

Step 3 Step 3 Lesson 1Displacement of

Liquids50 min

• When an object is fully submerged it displaces a volume of liquid equal to its own volume.

• When an object is partially submerged it displaces a volume of liquid equal to the volume of the portion of the object that is submerged.

• Scientists use multiple methods to calculate volume.

Step 3 Lesson 2Challenge #2 –

Irregular Shapes 50 min

• When an object is fully submerged, it displaces a volume of liquid equal to its own volume.


Step 4 Step 4 Lesson 1Exploring Apparent Weight & Buoyancy

50 min

• Gravity pulls down on all objects and accelerates them at a rate of 9.81 m/s2.

• The buoyant force pushes up on all objects and depends on the submerged volume of the object.

• Objects float if the buoyant force is larger than the gravitational force and sink if the gravitational force is larger than the buoyant force.

Step 4 Lesson 2A Balance of Forces

50 min• Buoyancy is determined by differences between the

gravitational force and the buoyant force.

Step 4 Lesson 3Predicting Payloads

50 min• Materials more dense than the liquid they are

submerged in can still float, just use balance of forces in design

Step 5 Step 5 Lesson 1Liquids and Buoyancy 50 min

• The density of liquids affects the buoyancy of objects submerged in those liquids.

• Temperature affects the density of fluids.

Step 5 Lesson 2Gases and Buoyancy 50 min

• The principles of density apply to gases as well as to liquids, and it affects the buoyancy of objects in those gases.

Step 6 Step 6 Lesson 1Evaluation:

Misconceptions and Oil Spills

50 min

• Density and a balance of forces determine whether or not an object will float.

• Common misconceptions can be addressed using evidence-based explanations.

Step 6 Lesson 2Inquiry into Density

and Buoyancy50 min

• Scientific investigations are usually directed by a specific testable question and involve collecting relevant evidence and using logical reasoning to develop evidence-based explanations.

Unit Overview 1�

Unit Content BackgroundWhether drinking from a glass of iced tea, swimming in a pool, boating on a lake, or studying the surface of Earth itself, the concepts of buoyancy and density permeate everyday life. Density, a measurement of the amount of matter contained in a given space, is an intrinsic property of materials under stable conditions and is a large part of the solution to figuring out whether things float or sink. Buoyancy, a balance of forces between the weight of objects and pressure from a surrounding fluid, factors into the rest of the explanation for floating or sinking objects. Taken together, the two concepts explain everyday occurrences like why ice, (most) people, and boats float on water and why Earth’s crust is made the way it is with rocks of a certain density, less than that of other parts of the interior of Earth.

There are many common misconceptions about buoyancy and density. These include ideas such as “all wood floats,” “heavy objects always sink,” and others about related concepts of forces and properties of materials that determine whether they float or sink. Throughout this unit, there are opportunities for students to test their conceptions of density and buoyancy and confirm or refute their ideas through investigation and experimentation.

Unit InvestigationThis unit’s investigation involves a series of student-directed inquiries that take place over the course of the unit to answer the question, “What makes things float?”

Students begin the unit by developing and then refining questions after observing sets of discrepant events involving density and buoyancy. These student-developed questions are systematically referenced after each mini-inquiry into the properties that affect density and buoyancy. In this way, students can evaluate evidence gathered in light of possible explanations for their questions while developing a way of knowing how to decide what makes things float.

What Makes Things Float? Unit Level Graphic OrganizerMany lines of evidence work together to explain what determines whether an object will float or sink in a particular fluid under particular conditions. This unit uses a graphic organizer to help students visualize how all this evidence fits together. The What Makes Things Float? graphic organizer is used throughout the unit, and evolves as students gather more evidence that supports understanding of buoyancy and density.

The example on the following page shows how the Unit Level Graphic Organizer may look at the end of this unit. (Note: For each lesson that references the chart, there is an example chart in the Implementation Guide that illustrates how it may look at that specific point in the unit.)

1� Buoyancy and Density: What Makes Things Float?

What Makes Things Float? ChartWhat did we do in this lesson?

What evidence did we collect?

Big idea(s) I took away from the lesson

How would you use that evidence to make a

prediction?

Measured mass of and floated cubes

Mass of the cubes and whether they floated

Heavy things sink, light things float

Weigh an object before predicting

It is not true that “All wood floats” or “All plastics float”

Measured mass of different cube combinations and floated them

Mass of cube combinations and whether they floated

Measuring mass or weight doesn’t seem to be quite enough information to always predict correctly whether a group of cubes will float.

Not sure. We need to know more to always make accurate predictions.

It is harder to predict if combinations of cubes will float than to predict if a single cube will float.

Rate of sinking can be changed because cube combinations sink at different rates.

Plotted data points on a graph of mass and volume

For everyone in the class, cubes sank when they were above a certain space on the graph and floated when they were below it.

There are patterns in the graph of our class data that may help to predict if something will sink or float

Analyzed plotted data points on a graph of mass and volume

The mass-to-volume ratio of objects that sink in water is greater than the density of water.

Measuring and calculating the ratio of mass to volume for an object makes it easy to predict if the object will sink or float in water.

Observed and measured the amount of “overflow” fluid from the container

Volume of “overflow” fluid

Objects that sink raise the fluid level in their container

Not sure. Volume is related to density but it alone cannot be used to predict whether an object floats.

One way to find the volume of an irregularly-shaped object is to measure the volume of fluid it displaces

Unit Overview 1�

Felt the forces needed to sink floating cubes and ping-pong balls

Qualitative measurement of forces

Ping-pong balls “push back” with a greater force than floating cubes when you hold them under water.

Not sure. Knowing the amount of “push-back” force may help predict if an object will float.

Used a spring scale to measure the weight of objects in water and air

Weight of objects in water and air

Sinking objects must have an upward force on them that makes them appear to weigh less in water than in air

Different liquids and gases seem to “push back” in different ways.

Objects that sink weigh less in water than they do in air

Observed objects floating on the surface of liquids

Whether objects float or sink in liquids

There is a balance of forces on floating objects

Not sure. The liquid has something to do with whether objects float.Floating objects remain at

rest where they float

Observed oil and water together in one container

Oil floats in water Liquids can have different densities, not just solids

Measuring the density of a liquid helps predict if it will float on another liquid.

Analyzed plotted data points on a graph of mass and volume (density)

Liquids can have different densities, not just solids

If you are working with a pure liquid (or solid or gas), it is possible to know what the density is by looking it up or measuring it just once, because it is a property that stays the same for a pure substance.

The mass-to-volume ratio of liquids that float (or sink) in other liquids is greater than (or less than) the m/V ratio of the other liquids

Read a story about methane gas in the ocean

The density of gases like methane and air

Gases can have different densities too!

Gases that are less dense than the fluid they are in will always float. Gas bubbles rise in liquids

The same gas can have different densities depending on the temperature

Hot air rises because it is less dense than cooler air.


Support MaterialsImmersion Unit Toolbox and CDThe Immersion Unit Toolbox is central to this curriculum. It is a separate guidebook that discusses the concepts inherent in teaching science through immersion units. These concepts include engaging in scientifically oriented questions, giving priority to evidence in responding to questions, and formulating explanations from evidence.

The Toolbox also describes several pedagogical approaches (Think-Aloud strategies, for example) that are key to how these units work. Most of the strategies in the Immersion Unit Toolbox support student engagement in scientific inquiry based on the Five Essential Features of Classroom Inquiry (NRC, 2000).

Before you use What Makes Things Float? in your classroom, it is recommended you become familiar with the strategies addressed in the Immersion Unit Toolbox.

This Immersion Unit comes with a data CD containing multimedia files for use at various points throughout the unit. It also contains resources and links to reputable Web sites that students can use during their region investigation. A CD icon in this unit highlights the points where many of these materials are referenced in the lessons.

Here is a brief overview of some of the strategies you can use in your classroom.

Science Inquiry Map The Science Inquiry Map on the following page illustrates the Five Essential Features of Inquiry. You can use this map in your classroom when you introduce Immersion Units to your students.

The science inquiry process is dynamic and does not necessarily follow a linear order. For example, a student may develop an explanation that leads to a new scientific question, or that student may revisit evidence in light of alternative explanations. On some occasions, multiple features of an explanation may overlap, or, depending on the type of lesson, some features may have more emphasis than others. These variations allow learners the freedom

to inquire, experience, and understand scientific knowledge. The Five Essential Features of Inquiry describe how engaging in science inquiry unfolds in the classroom.

Student GroupsIn this unit, students often work in groups. When working as a team in a group, the ideal is to have groups no larger than four students. Whatever the group size is, all students in the team need to have a job to do so they are individually accountable for focusing on the current science lesson. More information and suggestions for choosing groups is provided in specific lesson implementation guides.

Think Aloud StrategyWhat Makes Things Float? uses the Think Aloud strategy throughout the unit. The Think Aloud is a teaching approach whereby the teacher makes important thinking and reasoning processes explicit for learners by describing aloud the thinking process involved in a certain activity. In this way, the teacher makes visible to students the otherwise invisible thought processes that are essential for scientific reasoning to occur. Example Think Aloud dialog suggestions are included in the lessons that recommend using this strategy.

Think-Pair-ShareThink-Pair-Share is a cooperative learning technique that allows students to think before they respond to a prompt, to test their response on their partner, and then to share their response (possibly revised) with a larger group. Specific instructions for implementing the Think-Pair-Share strategy are discussed in the Immersion Unit Toolbox. What Makes Things Float? uses this technique throughout the unit.

REAPSREAPS is a method of formative assessment that combines the time-tested ideas of Blooms Taxonomy with new research on student assessment. The level of thinking increases from basic recall to complex analysis and predictions. On each Lesson Snapshot page is a series of REAPS prompts. This series of prompts is a simple tool that can be used throughout or at the end of each lesson. They

Unit Overview 17


can be used individually, in pairs or in groups to review what students know and are able to do. This provides an opportunity for the teacher to modify instruction as necessary based on student responses.

Here are the types of prompts included in the REAPS.

R Recall new knowledge: Determines whether the student has learned the basic knowledge that is related to and supports the key concept including lists, drawings, diagrams, and definitions.

E Extend new knowledge: Determines whether the student can organize the basic knowledge related to the key concept such as compare, contrast, classify.

A Analyze knowledge: Encourages the student to apply or interpret what they have learned including developing questions, designing investigations, interpreting data.

P Predict something related to new knowledge: Engages the student in thinking about probable outcomes based on observations and to engage

them in a new topic that builds on prior knowledge.

S Self/Peer Assess: Encourages students to take responsibility for their own learning. Includes methods and/or activities for students to assess their own learning and/or that of their peers.

The prompts increase in cognitive difficulty with Recall as the easiest and Predict as usually the most advanced. Students most likely demonstrate confidence and ability when responding to the first few prompts, while demonstrating continuous improvement in responding to the Apply and Predict prompts. Students are not expected to master all of the skills, but are encouraged to extend their thinking.

Suggested responses are included in italics after the prompts. While the suggestions are good responses, other responses may be just as good or worth recognition if they include appropriate supporting evidence and reasoning.

Step 1 Overview 19

Overview

Students’ initial curiosity about key concepts in density and buoyancy is stimulated by a series of “Float Demos” which contain odd pairs of floating and sinking objects. Students are encouraged to make and record observations and raise questions. In the second lesson, students will learn how to develop testable questions.

They will be guided to focus their initial questions into scientifically testable ones that can be explored through this Unit.

S T E P

1

Step1 Lesson 1: Floating Puzzles 21

Key Concepts• Scientists observe natural

phenomena, pose questions, and wonder based on their observations.

Evidence of Student UnderstandingThe student will be able to:

• observe the floating puzzles and develop questions about what they see related to the question, What makes things float?

Time Needed50 minutes

MaterialsFor each student:• science notebook• 1 copy of Student Page 1.1A:

Floating Puzzles

For each group of 4–6 students• 1 transparent container deep

enough for pairs of objects to float in water

• Float Demo materials Demo 1: diet and regular soda

cans (12 oz. cans) Demo 2: two capped/sealed

plastic vials of different volumes but same mass and a balance to confirm the mass

Demo 3: wood and copper cubes from density cube set

For the class• prominently displayed banner

that reads: What makes things float?

Floating Puzzles1. Introduce to the whole class this Immersion Unit’s overarching question, What makes things float?

2. Divide the class into groups of four to six students and distribute to each student a copy of Student Page 1.1A: Floating Puzzles.

3. Explain the procedure the class will follow for observing and recording questions about each of the Floating Puzzles.

4. Guide student groups to explore as a class the first of the three Float Demos.

• Have students record on Student Page 1.1A: Floating Puzzles or in their science notebooks the observations they make and questions that arise.

• Stop and discuss as a class the types of observations and questions students are making to help prompt students to think of additional ideas.

5. Repeat the procedure for making, recording, and discussing observations and questions for the other two Float Demos.

6. Have student groups review their questions and observations about the Float Demos. From the questions recorded, instruct each group to select three questions that they find most interesting, and write them on a transparency or post them in a designated location where they will remain throughout the unit (though they will be revised and rearranged).

7. Introduce the What Makes Things Float? Chart, and work as a class to complete a row based on Lesson 1 experiences.

8. Use the REAPS questions throughout the lesson where appropriate.

Step 1 Lesson 1 Snapshot



REAPS QuestionsR What pair of floating/sinking objects were you

most curious about? Students’ responses to this question may help you gauge their prior knowledge about density and what makes things float.

E What other floating or sinking objects have you observed in your everyday life? Students may recall floating a toy in the bathtub, being in a boat, a sponge floating in dishwater, or any other number of typical experiences.

A Students will analyze their observations and questions in later lessons.

P What do you think is important to notice to predict if something will float or not? Use this question to assess students’ preconceptions about factors that determine if an object will sink. Students may predict at this time, for example, that how heavy an object is determines if it will float.

S What did you think about today that you had not thought about before? Prompt students to reflect on what they wondered as they made observations.

Step1 Lesson 1: Floating Puzzles 2�

Teacher Background InformationIn this unit, students investigate and gather evidence to explain density as a property before using the term density. The unit opens with the overarching question that will underlie each lesson in the unit, What makes things float? Students’ are guided through a series of activities and lessons to first construct the evidence needed to explain the relationship between mass and volume as a property that makes it possible to predict what will float. Then, students continue to inquire and engage in readings and lessons to learn about buoyancy. The formulas for these properties are abstract and are intentionally omitted until later lessons, as students first engage in concrete experiences to identify the factors that influence whether an object will float or sink.

Science NotebooksDensity and Buoyancy is written with specific references for students to make entries in their science notebook. The use of science notebooks for each student is strongly encouraged for all science lessons, particularly those throughout

this unit. Specific opportunities for using science notebooks in this unit are explicitly described where appropriate. A bound notebook works well for a science notebook because its pages cannot easily be torn out or replaced, handouts and other loose pieces of paper can easily be taped in, and it is inexpensive.

Notebook entries can include written observations, labeled drawings, date, time, environmental conditions or weather, and even small samples pressed between the pages. The important thing to remember when drawing and/or writing for scientific purposes is to draw or write only about what can be directly observed.

Think-Pair-ShareThink-Pair-Share is a cooperative learning technique that is used frequently in this Immersion Unit. It allows students to think before they respond to a prompt, to test their response on their partner, and then to share their response (possibly revised) with a larger group. Specific instructions for implementing the Think-Pair-Share strategy are discussed in the Immersion Unit Toolbox.


Advance PreparationDensity CubesDensity cubes are used throughout this unit, although they are purposely not referred to as density cubes before Step 3 because students develop an understanding of density by engaging in a series of inquiries. In preparation for using these cubes, consider the following:

• Obtain enough sets of cubes to have at least two sets for every four students.

• If possible, use cube sets that include a wooden cube that sinks. Alternatively, it may be possible add a sinking wooden cube of the same size to your sets. While this is not necessary, it is a good way to help break the common misconception that all wood floats.

• Number the cubes with a fine-tip permanent marker, using the same number key for each set so that it is easy for the class to communicate about the cubes. Once the cubes become wet, the wooden cubes are particularly difficult to distinguish.

– Prepare a poster with the numbers and types of cubes they refer to so the students can refer to it throughout the unit.

• Consider waxing or varnishing the wooden cubes so that they do not absorb water and deteriorate.

– Any time the wooden cubes are used, have students remove them from the water and dry them off as soon as the trial is completed.

– Over time, the wooden cubes will change density by absorbing water and swell and split.

• If storing the cubes in their original container, remove or cover any reference to the word density. In this unit, students investigate and gather evidence to explain density as a property before using the term density.

• Refer to the cubes as blocks or cubes, not density cubes in class.


Step1 Lesson 1: Floating Puzzles 2�

Container for Floating ObjectsThroughout the unit, students will test a variety of cube combinations and some other objects to see if they float. For each group of 4–6 students, provide at least one transparent container of water that can be used for each of these investigations. You may consider several options for this equipment:

• 1000 ml beaker• small aquarium• clear 2-liter soda bottle with top cut off• other recycled clear plastic containers or glassware that is large enough for

students to reach a hand into and sink 4–5 cubes banded together

Floating Puzzle PreparationsPrepare in advance materials for the Float Demos to be observed by groups of 4–6 students. Students will observe and ask questions about each puzzle, working as a class on each puzzle before moving on to the next. Student Page 1.1A: Floating Puzzles provides a format for recording observations and questions; plan for having copies of this page for each student or you may wish to have them copy a similar format directly into their science notebooks.

Demo 1: Two soda cans (one diet and one regular) in a deep transparent container filled with water. The 12 oz. cans work most consistently. The demo will look something like the following:

• Diet soda can floats • Regular soda can sinks

Test cans in advance because canning errors sometimes result in non-consistent behavior. When placing cans into the water, be careful to tip each can slightly to avoid capturing a bubble of air in the bottom, concave end of the can.

Demo 2: Measure and fill two capped/sealed vials with table salt or sugar so that they have different volumes but the same mass. Use small plastic vials with caps. Select vials that are obviously of different size. If possible, use vials that are transparent so students see contents plus air pocket. A plastic coin tube and empty medicine bottle are used in the sample photo. Add a solid (like salt or sugar) such that the total mass



of vial, cap and contents are the same for both vials. Cap tightly and place these in a container of water. Provide a balance so that students can confirm that the mass is the same for both vials.

Demo 3: A container of water with two density cubes. One cube is made of wood and the other of metal (brass or copper). If available in your density cube sets, use the wooden cube that sinks to cause students to wonder about any preconceptions they may have that all wood floats.

What Makes Things Float? ChartThroughout this unit, students are prompted to make note as a class about what was observed and learned from a lesson. It is important to provide this continuity to keep track of the big explanation that students are developing over several weeks—they are gathering evidence and building their understanding of the properties that determine whether an object will sink or float. This graphic organizer offers a concrete method for tracking that progress.

It is recommended that you both keep a classroom copy of the chart and have students keep a copy in their science notebooks. Decide in advance the logistics for doing this. You may wish to make the classroom chart on an overhead transparency if it is challenging to post it on the wall. If you are able to post the chart, it will be easier to refer to it on a regular basis; however, you will need to manage a way to keep from displaying an earlier class’ chart to a later class.

The What Makes Things Float? Chart has the following headings:

What Makes Things Float? Chart

What did we do in this lesson?


Big idea(s) I took away from

the lesson

How would you use that evidence

to make a prediction?

Step1 Lesson 1: Floating Puzzles 27

Implementation Guide1. Introduce to the whole class this Immersion Unit’s overarching question, What makes things float? Explain that throughout this unit the students will be conducting investigations and lessons to help them explain what makes things float. Today, they will begin by observing some interesting pairs of floating and sinking objects.

2. Divide the class into groups of four to six students and distribute to each student a copy of Student Page 1.1A: Floating Puzzles.

3. Use the student page to explain the procedure the class will follow for observing and recording questions about each of the Floating Puzzles. Highlight the importance of making detailed observations and recording all the questions that arise. Instruct students to minimize water spillage and not to open any of the containers.

4. Travel around the room and guide student groups to explore the first of the three Float Demos.

• Have students record on Student Page 1.1A: Floating Puzzles or in their science notebooks the observations they make and questions that arise.

• Stop and discuss as a class the types of observations and questions students are making to help prompt students to think of additional ideas.

5. Repeat the procedure for making, recording, and discussing observations and questions for the other two Float Demos. Encourage students to make

comparisons among the Float Demos and revisit a demo if needed.

6. Have student groups review their questions and observations about the Float Demos. From the questions recorded, instruct each group to select three questions that they find most interesting. Make the questions visible to all students by either recording them on a wall chart or overhead transparency displayed for the class.

As questions are posted, sort them for duplicates and roughly group them by similarities. These questions will be addressed in the next lesson and throughout the unit.

• Include all questions and statements at this point without correcting misconceptions or probing for answers.

• These are initial questions; expect many to be elementary or to reveal misconceptions.

7. Introduce the What Makes Things Float? Chart. Explain that this chart, along with their question wall, will be the focal points for the unit. The class will keep track of their work and learning about how to explain what makes things float. This chart will be dynamic so, students can change and add to it as their knowledge grows and changes. Work as a class to complete a row based on Lesson 1 experiences. This is an example of how the chart may look after this lesson:


What Makes Things Float? Chart





prediction?

Looked at Float Demos Observations Some things are hard to predict if they

will float or not.

Not sure

Student Page 1.1A: Floating Puzzles 29

Student Page 1.1A: Floating Puzzles

Directions Observations: Make observations on the puzzle on your table. Watch what is happening and write everything you see. Details are very important! You may also talk to your team members about what you see.

Questions: After completing your observations, write down as many questions as you can about the puzzle you just observed. Base your questions on your observations.

Puzzle #1: CubesObservations:

Questions:

Puzzle #2: VialsObservations:

Questions:

Puzzle #3: Soft drink cansObservations:

Questions:

�0 Buoyancy and Density: What Makes Things Float?

Step1 Lesson 2: Crafting Testable Questions �1


Key Concept• Scientists observe

natural phenomena and develop testable questions based on their observations


• identify questions that are testable in the classroom from a list of testable and non-testable examples.

• convert initial wonderings about the floating puzzles into testable questions.


MaterialsFor each student:• 1 copy of Student Page

1.2A: Questions for Investigations

For the class• list of questions

generated during Lesson 1.1 (either on transparency or posted on the wall)

REAPS QuestionsR Name one question that we discussed that is not

readily testable in our classroom? Explain why it is not testable. Look for students to be able to explain that a testable question in this context needs to suggest an investigation that can be conducted using the equipment available in the classroom.

E Why is a question sometimes not “testable”? What does that mean? Some questions are not testable because they do not lend themselves to experimentation. Being testable means that an answer to the question can be found based on measurable observations.

A How are “testable questions” related to “variables”? Testable questions can be investigated, which means that the question asks about variables that can be controlled and/or manipulated, measured and/or observed.

P Which of the questions developed by your class do you think will be the most challenging to answer? Why do you think so?

S How did working on questions during this lesson change the way that you think about what makes things float?

Crafting Testable Questions1. Point to the What Makes Things Float? question that is guiding this unit, and reflect back on both the student questions from Lesson 1.1 and the What Makes Things Float? Chart. Explain that in this lesson the class will think more about questions they are wondering (stimulated by the floating demos), to consider the following:

• Are the questions related to the overarching question, What makes things float?

• Are their questions testable?

2. Distribute Student Page 1.2A: Questions for Investigations, and use a Think-Pair-Share strategy for students to complete and review the exercise.

3. Apply the same strategies as used on Student Page 1.2A: Questions for Investigations, to have students refine their questions and statements from Lesson 1.1 to be testable questions. Give students the opportunity to contribute additional questions as they arise, too.


Step1 Lesson 2: Crafting Testable Questions ��

Teacher Background InformationSeveral common misconceptions about density and buoyancy may surface during the discussions in this unit. For example, one might think that things float because they are made of wood and things sink because they are made of metal. However, many people know that wooden boats can sink and that boats made of metal (tankers, military boats) can float. If this kind of discussion appears during the class discussion about their questions, make note of the misconception to be certain it is addressed by the end of Lesson 2.3, and resist providing an answer at this time.

During this and the previous lesson, students are engaging in thinking about what makes things float and beginning to explore and observe demonstrations that the class can have in common to discuss. In the next two lessons, students will gather evidence to use in developing an explanation for density in Lesson 2.3. This is an intentional design—for students to start with concrete examples of objects floating, explore variables that they likely think affect if an object floats, and then look for patterns in their evidence to explain the abstract concept of density.

�� Buoyancy and Density: What Makes Things Float?

Implementation Guide1. Begin a class discussion with the list of student questions from Lesson 1 posted as sentence strips, on a chart, or overhead slide (choose a method that makes it easiest for all students to see the questions).

• You may want to provide at least one sample of the three Float Demos for reference.

• Remind students of the overarching Immersion Unit question What makes things float? and revisit the What Makes Things Float? Chart to bridge what students did in the previous lesson with revisiting questions in this lesson.

2. Distribute Student Page 1.2A: Questions for Investigations, and use a Think-Pair-Share strategy for students to complete and review the exercise.

• What Makes Things Float?

3. Ask students to apply their learning about testable questions to the questions they generated during the last lesson. Take the questions or statements in order and ask students to consider if each one.

• addresses the overarching question

• is testable

If a question or statement does not meet these criteria, ask students for suggestions on how they could modify it to make it fit. The results of this discussion will depend on the list of questions and statements the students produced. Work through the questions and statements as a lesson in reasoning and in crafting questions that can be tested. Select one or two at the end that lead into Step 2. Examples include questions like the following:

• How does weight of an object affect its ability to float? (or similar questions related to the weight or mass of an object)

• Does the shape of an object determine whether it floats?

• Can something that sinks hold down something that floats?


Student Page 1.2A: Questions for Investigations ��

Part A: In science, we investigate scientifically oriented questions. These questions need to be testable. Which of the questions below are good testable investigation questions?

Circle all the testable questions. Be prepared to explain what makes you think they are testable.

Student Page 1.2A: Questions for Investigations

1. What would a crayfish do on the moon?

2. Why is the inside of Earth hot?

3. What would happen if we put an apple and a banana in a warm wet environment? Would one rot faster than the other?

4. Why do those plants have yellow flowers?

5. Why do snails climb on some rocks and not others?

6. How many wood cubes do you have to add to a silver cube to make it float in water?

7. Why does it rain during baseball games?

8. Where would a crayfish go if we added another crayfish to its tank?

9. Will increasing the amount of light a plant has make it flower faster?

Part B: What patterns do you notice in the testable and non-testable questions?

Testable Questions Non-Testable or Difficult to Test Questions

What kinds of “question” words are used?

What kinds of materials are needed?

Could you design an investigation to answer this question in class?

Part C: Testable questions typically have certain characteristics. What would you look for in a testable question?

_______________________________________________________________________________________

_______________________________________________________________________________________

Part D: Change 3 of the non-testable questions above into testable questions.

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

Teacher Page 1.2a: Questions for Investigations �7

Part A: In science, we investigate scientifically oriented questions. These questions need to be testable. Which of the questions below are good testable investigation questions?

Circle all the testable questions. Be prepared to explain what makes you think they are testable.

Teacher Page 1.2a: Questions for Investigations

1. What would a crayfish do on the moon?

2. Why is the inside of Earth hot?

3. What would happen if we put an apple and a banana in a warm wet environment? Would one rot faster than the other?

4. Why do those plants have yellow flowers?

5. Why do snails climb on some rocks and not others?

6. How many wood cubes do you have to add to a silver cube to make it float in water?

7. Why does it rain during baseball games?

8. Where would a crayfish go if we added another crayfish to its tank?

9. Will increasing the amount of light a plant has make it flower faster?

Part B: What patterns do you notice in the testable and non-testable questions?

Testable Questions Non-Testable or Difficult to Test Questions

What kinds of “question” words are used?

What, will, how, does, where, can Why

What kinds of materials are needed?

Materials that can be found in the classroom or brought from home

Materials that are difficult to get—too expensive, not yet invented, etc.

Could you design an investigation to answer this question in class?

Yes No

Part C: Testable questions typically have certain characteristics. What would you look for in a testable question?

Look for questions that can be explained through an investigation with measurable results and be the type of investigation that can be conducted in our classroom with our materials.

Part D: Change 3 of the non-testable questions above into testable questions.

Does the moon environment supply what a crayfish needs to live?

How do scientists know that Earth’s interior is hotter than the surface?

If the yellow flowers are removed from those plants, will they still reproduce?

Do snails choose to climb on river rock over rough granite when given the choice?

Does it rain during ball games more often than not?

Step 2 Overview �9

S T E P

2

Overview

In Step 2, students discover for themselves the relationship between volume and mass for the density of solid objects. By gathering evidence about floating and sinking objects before being introduced formally to the concept of density (or the formula), students experience concrete connections to mass and volume being factors in determining what floats before being asked to understand the abstract notion of density.

Lessons 2.1 and 2.2 engage students in making observations about cubes that sink and float that are later used to explain density. Students gather information about the mass and ability to sink or float for a number of single- and multi-cube objects, and then that data is graphed to reveal patterns for predicting what will float. When they graph their results and perform a careful analysis with the teacher’s assistance, the data reveals a linear relationship between mass and volume. The slope of that line is then explained as density.

In Lesson 2.4, students explore how density is an intrinsic property and does not change under stable conditions if a material is divided into parts. By the end of Lesson 2.4, students will have the tools to be able to explain the two soda cans and vials of different volume from the opening Float Demos. The first Challenge Problem to check for students’ ability to apply their understanding to a new situation occurs in Lesson 2.5.

Step 2 Lesson 1: Mass and Floating �1


Key Concepts• Scientists use precise measurements

to make accurate explanations. • Heavier cubes are more likely to sink

than lighter cubes (of equal volume).


• make, record, and understand both qualitative and quantitative observations accurately while experimenting with cubes that sink and float;

• continue to develop questions and make initial evidence-based predictions about what determines if an object will float.


MaterialsFor each student• 1 copy of Student Page 2.1A:

What Makes Things Float? Data Collection Sheet #1

For each group of 4–6 students• 2–3 sets of (density) cubes (Note:

Do Not refer to these as “density” cubes with students as their inquiry with the cubes leads to exploration of density)

• calipers and/or rulers• other measuring devices such as

thermometer, graduated cylinders of various sizes, pH paper or whatever is available in your class

• balances capable of measuring mass up to 200 grams (electronic or triple beam balance)

• 1 large container of water in which cubes can float

REAPS QuestionsR What is the definition of a quantitative

observation? A quantitative observation is one that can be measured. In other words, you can assign a number (quantity or amount) to the observation.

E What is one factor that seems to affect whether an object is likely to sink or float? What evidence do you have that supports your idea? Mass (or weight) is likely the only factor that students will be able to explain with evidence from the class data.

A Explain if the following statement is quantitative or qualitative: The copper cube sunk quickly to the bottom. This is a qualitative statement about the speed with which the copper cube sank because the speed was not measured directly.

P If you had another set of cubes that were just the same as those you have now except they were all two times bigger, would the same kinds of cubes float as what you observed in this lesson? Yes. At this point, students have not been introduced to density being a standard property of solids, but they may make the connection that the same materials would behave the same way.

S How have your ideas about how to predict what will float changed?

Mass and Floating1. Introduce the lesson and review the question wall from the previous Step in light of the overarching question, What makes things float?

2. Familiarize students with the materials they will have.

• cube sets

• tanks of water

• a variety of measuring tools (whether or not they pertain to density)

3. Direct students to work individually to record in their science notebooks or on Student Page 2.1A: What Makes



Things Float? Data Collection Sheet #1 and answer to the following question:

• What data will you need to collect and record to accurately predict if a cube will sink or float?

4. Hold a whole-class discussion about the types of observations students plan to make. List suggestions from student volunteers, then use a Think-Pair-Share strategy for students to explain what they know about which are quantitative and which are qualitative observations.

• Provide definitions if students are unable to offer correct definitions (see Teacher Background Information).

• Explain that there is one quantitative measurement that you want all students to observe and record so that the class can share data: mass (in grams).

• Explain the data table in Student Page 2.1A or have students make a similar table to record data in their science notebooks.

5. Form the class into groups of four or six students (depending on the number of cube sets available).

• Have student groups make and record observations (either in their science notebooks or on Student Page 2.1A: What Makes Things Float? Data Collection Sheet #1.

• Explain that students will be reporting both observations and measurements taken to the class after a 15-minute exploration time.

6. Give the class 15 minutes to make and record observations and measurements.

7. As a whole class, collect and record from each group one qualitative and one quantitative observation.

• With each measurement, record whether the cube sank or floated.

8. Guide a discussion to look for patterns in their data. During the discussion, be sure that students reference the class data.

• Look for students to recognize that the cubes with greater mass sink. This is a quantitative measurement that can help predict if an object will float.

– Resist the temptation to introduce volume as another determining factor unless students raise that idea in the discussion.

• Be certain students also recognize that not all cubes sink or float the same (some sink more quickly, some float higher in the water), and that qualitative observations are important, too.

9. Refer the class to the What Makes Things Float? Chart, and record a new row based on the information learned during this lesson.


Step 2 Lesson 1: Mass and Floating ��

Teacher Background InformationQuantitative data are information that is recorded in numeric form. This kind of data is often represented in tables and graphs that show relationships between characteristics. For example, by counting the number of leaves on a plant, one creates quantitative data about the plant. This differs from qualitative data because a number, rank, or some sort of ordering or meaning is assigned to quantitative data. In other words, if you wanted to compare two plants, it is meaningful to refer to each by the number of leaves they have. Gathering quantitative data often makes it easier to compare two or more objects and find patterns in the data that describe some natural phenomenon.

Advance PreparationMake copies of the student pages, and check for equipment. The same containers that were used for the Float Demos can be used by groups to test objects during the next several lessons.

If the density cubes are not yet numbered, be sure to do so now so that the class can communicate their results effectively. A fine-tip permanent marker works well for this.

Consider making a poster showing the numbers assigned to the cubes and their descriptions so that the class can reference that poster during discussions. The poster could include a table like the following:

Qualitative and Quantitative DataOne can collect two kinds of data in most experiments: qualitative and quantitative. Both are important in science, but they are different in the following ways.

Qualitative data are information that is recorded using written descriptions and narrative information. This may include colors, textures, and behaviors of an object. For example, observations like “This plant is green, has shiny leaves, and feels soft,” are qualitative. They are not usually converted to a numeric form since they are most meaningful in that narrative form. It is often hard to assign a number or rank to qualitative data.

Number Cube Description1 Wood 12 Wood 23 Wood 34 Brass-colored5 Black6 Clear plastic7 Copper-colored8 Gold-colored9 Silver-colored10 White plastic


Implementation Guide1. Explain to students that in Step 2, they will begin exploring and gathering evidence that may be useful in explaining responses to the class questions and the overarching unit question, What makes things float? Point out the question wall developed by students in the previous step, and remind them of the Float Demos they observed.

2. Although it is known that measurements that pertain to density are the volume of the cubes (roughly the same for each cube) and the mass of the cube, the developers intentionally designed this lesson to have students state their own preconceptions about what makes things float and then discover the property of density through inquiry.

Familiarize students with the materials they will have.

• cube sets

• tanks of water

• a variety of measuring tools (whether or not they pertain to density)

3. Direct students to work individually to record in their science notebooks or on Student Page 2.1A: What Makes Things Float? Data Collection Sheet #1 an answer to the following question:

What data will you need to collect and record to accurately predict if a cube will sink or float?

• Writing down their predictions at this point is important for engaging students actively in reasoning and using logic to explain a phenomenon (floating objects) that might otherwise be taken for granted.

4. Hold a whole-class discussion about the types of observations students plan to make. Write a list on the board as students offer suggestions about what ought to be measured. Explain that some observations are quantitative and some are qualitative, and both are important. Next, use a Think-Pair-Share strategy for students to explain what they know about which are quantitative and which are qualitative observations.

• Provide definitions if students are unable to offer correct definitions (see Teacher Background Information).

• Remind students how many times the idea that how heavy something is affects whether it will float, so you want the whole class to make and record observations about that one quantitative measurement so that the class can share data: mass.

– Review as needed how to use the equipment available correctly and accurately to measure mass in grams.

• Explain the data table in Student Page 2.1A or have students make a similar table to record data in their science notebooks.

5. Divide the class into groups of four or six students. Fewer students means more time actively engaged; however, groups will need at least two density cube sets for the next lesson, and you may wish to have the same student groups work together for both lessons.

• You may want to have students work with a partner within their larger group to increase accountability and opportunities to manipulate the cubes.

• Explain that each student group will report to the class what they observed and the measurements taken at the end of 15 minutes. This is a brief report because all the data will be relatively similar.

6. Let groups investigate at will for 15 minutes, and then bring the class back together for some reporting.

• Circulate among student groups as they investigate and encourage accurate measurement and careful observation.

7. Collect from each group one qualitative and one quantitative observation, and record them where the whole class can see. With each measurement, also record whether the cube sank or floated. Group similar observations together as you record them.

Step 2 Lesson 1: Mass and Floating ��

8. Facilitate a whole-class discussion (possibly with small group discussion mixed in) for students to look for patterns in the data.

• Chart student data on a large table similar to the one on Student Page 2.1A.

• Press students to base their analyses on the evidence at hand by asking: How do you know? Insist on specific references to class data as students suggest patterns.

• Be certain students also recognize that not all cubes sink or float the same (some sink more quickly, some float higher in the water), and that qualitative observations are important, too.

Note: Depending on what was measured by the class, there will likely be insufficient data to show that mass alone is not a good predictor for whether something will float or not. Most likely, at this point students will observe that heavy cubes sink and light cubes float (so mass IS the predictor for what will float). Begin to question them about the “size” of the cubes so that students at least notice that all the cubes are the same size. In Lesson 2.2, students will experiment with different cube combinations to bring the importance of volume to their attention.

9. Refer the class to the What Makes Things Float? Chart, and record a new row based on the information learned during this lesson. The chart may now look something like the one below.







prediction?


Mass of the cubes and whether they

floated



It is not true that “All wood floats” or “All

plastics float”

Student Page 2.1A: What Makes Things Float? Data Collection Sheet #1 �7

I predict that if I observe the following about a cube, I can accurately predict if it will sink or float.

_______________________________________________________________________________________

_______________________________________________________________________________________

Cube # My Prediction

(S or F)

Quantitative Measurements

Qualitative Observations Mass (grams)

Test Results(S or F)

Student Page 2.1A: What Makes Things Float?

Data Collection Sheet #1

Step 2 Lesson 2: How Heavy? �9


Key Concepts• Two different-sized objects made

of the same material sink or float the same way.

• Heavy things may float or sink depending on their size.


• recognize that mass is helpful for predicting whether an object—even a complex object—will float;

• explain that mass is not sufficient to predict if a multi-block combination will float.


MaterialsFor each group of 4–6 students• 2–3 sets of cubes (Note: Do

Not refer to these as “density” cubes with students as their inquiry with the cubes leads to exploration of density)

• 4 large rubber bands• calipers and/or rulers• balances (double balance and/or

graduated or electronic scale)• large container of water in which

cubes can float• towel to clean up spills

REAPS QuestionsR What unit do we use to measure mass? grams.E What is one qualitative observation that you

made while testing multi-cube combinations? Students may have observed that the heavier cubes in the cluster rotated downward as the object sunk (or floated); they may have observed the relative speed at which the cubes sunk, or they may have observations about the colors of the cubes.

A Explain if knowing the mass of an object is enough to predict if a multi-cube combination will float. Just knowing the mass of an object is insufficient for accurately predicting if an object will float.

P Is it possible that a cube that sinks in water would float in another liquid? Explain your answer. Some students may recognize that a cube that sinks in water might float in another liquid if the other liquid has a greater mass to volume ratio than water.

S Were more of your predictions correct or incorrect about which cube combinations would float? Explain why.

How Heavy?1. As a whole class, review the Question Wall and solicit answers, additions, and/or modifications to the questions based on what the class has reported learning on the What Makes Things Float? Chart.

2. Challenge the class to consider what would happen if cubes were combined. Prompt students to explore testable questions, such as: “Do two floaters attached together still float?”

“Do two sinkers still sink?” “What about a combination of sinking and floating?”

3. Have students work individually to plan for interesting cube combinations and predict the results.

4. Instruct students to work with a partner in the groups from Lesson 2.1 to conduct trials and record observations. Explain



that there is a time limit (approximately 30 minutes) for gathering information about the mass of the following:

•4 combinations of 2 cubes in which at least 1 combination floats and 1 sinks;

•4 combinations of 3 cubes in which at least 1 combination floats and 1 sinks;

•4 combinations of 4 cubes in which at least 1 combination floats and 1 sinks.

Circulate around the class and ask questions that will encourage students to at least measure and record the weight of their cube combinations.

5. Add a row to the What Makes Things Float? Chart to reflect what students learned from this lesson.


Step 2 Lesson 2: How Heavy? �1

In Lesson 2.2, students combine cubes of the same and different material and test to see if they float or sink. Combinations of floaters (wood) and sinkers may or may not float. For instance, wood #2 + white cube have a mass of 31.3 g (including the rubber band) and they float. Wood #2 + black cube have a mass of 34.1g and barely floats (with wood at the surface of the water). But wood #2 + silver-colored cube with mass of 54.9 g sinks.

As students move on to try three and four cubes together, the class will produce data tables like that shown below. The particular values shown here reflect the combinations we measured. Students will have other combinations, but they should be able to see values for floating and non-floating combinations. This data will be graphed and analyzed in Lesson 2.3 to develop an explanation for density.

Mass (g)

1 Cube 2 Cubes 3 Cubes 4 Cubes

Float 6.7 15.9 30.1 57.3

8.3 20.2 38.4 62.2

12.3 22.1 41.4 64.7

27.6 44.7 65.9

31.3 69.3

34.1

Sink 17.7 38.6 63.4 70.6

20 42.4 65.3 73.9

23.7 52.7 158.3 75.5

44.1 54.9 86.2

125.7 136

137.3

144.1

Teacher Background Information


Advance PreparationPlan the following in advance:

• how you will group students (same as Lesson 2.1 or new groups)

• how much time you will limit the investigation to so that students stay on task yet have sufficient time to run their trials

• what you will use to hold water so that cube combinations can fit easily (Keep in mind that water in the tubs must be deep enough to accommodate the size of multi-cube combinations. If a cube group rests on the bottom with a corner protruding from the water, students cannot say whether the group sinks or floats.)

Step 2 Lesson 2: How Heavy? ��

Implementation Guide1. As a whole class, review the Question Wall and solicit answers, additions, and/or modifications to the questions based on what the class has reported learning on the What Makes Things Float? Chart.

2. Initiate the next investigation by holding up a rubber band and asking, What happens when you combine cubes? Prompt students to refine this to be a testable question, such as:

• Do two floaters attached together still float?

• Do two sinkers sink?

• What about a combination of sinking and floating?

3. Direct students to individually record in their science notebooks different cube combinations and what they predict the result will be if they run a trial. Suggest a table like the sample below, to record these predictions and then results.

4. Instruct students to work with a partner to conduct their cube combination investigations. You may want to begin with 20 minutes and then check in with students to see if more time is needed to gather results for all combinations individual students planned. Structure the data collection to guarantee that the class generates sufficient data points to clearly see the line between sinkers and floaters

when the data is graphed. Have pairs select, predict, measure and test:

• 4 combinations of 2 cubes in which at least 1 combination floats and 1 sinks;

• 4 combinations of 3 cubes in which at least 1 combination floats and 1 sinks;

• 4 combinations of 4 cubes in which at least 1 combination floats and 1 sinks.

Direct students to return to their groups from Lesson 2.1 (or you may wish to rearrange groups) and begin trying out their combinations and recording observations.

• As you circulate around the class, remind students that they should conduct multiple trials as needed to collect both quantitative and qualitative observations.

• Ask to see students’ data tables to both informally assess their current understanding of buoyancy (by reading the predictions) and track the types of quantitative measurements being made.

• Ask questions that will encourage students to at least measure and record the weight of their cube combinations.

cube mass measurement or observation 2:

I predict it will (S or F)

actual obs. (S or F)


5. Add a row to the What Makes Things Float? Chart to reflect what students learned from this lesson. The chart may look something like the following at this point:






prediction?






plastics float”

Measured mass of different cube combinations and

floated them

Mass of cube combinations and

whether they floated

Measuring mass or weight doesn’t seem to be quite enough

information to always predict correctly

whether a group of cubes will float.


It is harder to predict if combinations of cubes

will float than to predict if a single cube will

float.

Rate of sinking can be changed by combinations with different rates of

sinking.


Step 2 Lesson 3: Analyzing Data to Predict What Will Float ��


Key Concepts• Objects with a density less

than the density of water (1 g/cm3) will float in water at some level.



• identify the significant patterns in graphed data for sinker and floater cubes.

• recognize density as the slope of the line describing the mass to volume ratio for a substance.



Graphing Results• 1 copy of Student Page 2.3B:

Interpreting Data

For each group of 4–6 students• 1 overhead transparency of

Student Page 2.3A: Graphing Results

• 2 overhead transparency pens of different colors (each group needs the same 2 colors)

For the teacher• Teacher Page 2.3c: Think Aloud

Notes for Analyzing Results

Analyzing Data to Predict What Will Float1. Have student groups take out and review their work from the previous lesson, gathering observations about cube combinations. Engage the class in thinking about different ways their data could be organized to look for different patterns. Explain how scientists often use graphs to look for patterns between two types of observations that seem related.

2. Have students graph their data for mass versus number of cubes on a transparency of Student Page 2.3A: Graphing Results.

• NOTE: Have the whole class use the same color pen for sinkers and the same color pen for floaters.

3. Have student pairs add the data for single cubes that they collected in Lesson 2.1 plus the multi-cube data from one other group to their graphs.

•This number of data points will be sufficient for students to begin to see a pattern in their data.

4. Use a Think Aloud Strategy to guide students to analyze the graphs produced by groups.

•See Teacher Page 2.3c Think Aloud Notes for Analyzing Results.

5. Revisit the What Makes Things Float? Chart and have the class contribute a new row that represents their learning from Step 2, so far.

6. Direct students to reflect on the list of questions recorded in Step 1, and ask if there are any evidence-based explanations stemming from the work in Step 2 that would help answer any of the questions. Solicit modifications to questions and/or new additions.

7. Use the REAPS questions in Student Page 2.3B: Interpreting Data to check for student understanding of the concept that the mass-to-volume ratio for an object determines whether it floats or sinks in a particular liquid.

REAPS Questions

See Student Page 2.3B: Interpreting Data for REAPS questions.

Step 2 Lesson 3: Analyzing Data to Predict What Will Float �7

Teacher Background InformationThese Immersion Unit Toolbox sections provide detailed information designed to help teachers understand the importance of each step in the process of explanation development and provide tips and strategies for facilitating this process with students, including:

• Giving Priority to Evidence in Responding to Questions

• Formulating Explanations from Evidence

• Connecting Explanations to Scientific Knowledge

• Communicating Results and Justifying Explanations

Developing Scientific ExplanationsIn this lesson, students are involved in developing a scientifically accurate explanation to one aspect of the overarching question, What makes things float? and in learning what makes a strong scientific explanation.

They begin by analyzing the data collected from their investigations into floating and sinking cube combinations and are guided to use that data to develop an explanation. Then, they evaluate that explanation in light of other scientific sources in Lesson 2.4. Finally, they apply, communicate, and justify their explanation for What makes things float? in the Milestone Challenge in Lesson 2.5. This explanation for how mass and volume can be measured and compared to predict if an object will float is a culminating experience for understanding density in this unit.

Advance PreparationBefore teaching this lesson, review Teacher Page 2.3c: Think Aloud Notes for Analyzing Results to prepare for the graph analysis in which you will guide students to explain that the ratio of mass to volume is what determines if something will float in a particular liquid. This lesson is the critical explanation development lesson for students to learn what density is.

For an additional resource about using the Think Aloud strategy to make the kind of logical reasoning that characterizes scientific understanding, see the Immersion Unit Toolbox.

For this lesson make transparencies of Student Page 2.3A: Graphing Results, and check to be sure that the transparency type is such that you can stack multiple copies together and display the data without it becoming too dark. In this lesson, class data is combined for analysis by carefully stacking and displaying each group’s data to make a larger pool of results for analysis.


Implementation Guide1. Have student groups take out and review their work from the previous lesson, gathering observations about cube combinations. Engage the class in thinking about different ways their data could be organized to look for different patterns. Students may suggest things like pie charts, data tables, and scatter plots.

Explain how scientists often use graphs to look for patterns between two types of observations that seem related. Engage students in a discussion about which observations they have been making that seem important for predicting what will float. Guide the focus to recognize mass and number of cubes as logical factors to compare using a graph.

2. Distribute a transparency of Student Page 2.3A: Graphing Results to each group and a paper copy to each student. Have student groups graph their data for mass versus number of cubes on the transparency and individual students graph their data on the paper copy.

• NOTE: Have the whole class use the same color pen for sinkers and the same color pen for floaters.

3. Explain that having additional data would allow them to more clearly see patterns in the data. Have student groups add the data for single cubes that they collected in Lesson 2.1 plus the multi-cube data from one other group to both their group and individual graphs.

•This number of data points will be sufficient for students to begin to see a pattern in their data.

4. Use a Think Aloud to guide students to analyze the graphs produced by groups. See Teacher Page 2.3c Think Aloud Notes for Analyzing Results.

• During the analysis, students are guided to recognize the significance of the boundary between sinkers and floaters—concrete evidence for understanding density as a property that determines if an object will sink or float in a particular liquid.

– In guiding students to look for patterns in the sinkers and floaters, you may want to talk about the two types as “groups” as separate and ask, “How could we

separate these groups?”

• When students are asked about what would happen if a cube of liquid water were placed in water, provide an opportunity to calculate points to add to the graph for the mass of water that would occupy the volume of one, two, three, and four cubes.

– First, have students find the volume of a cube, then use a graduated cylinder and balance to find the weight of that volume of water.

• Consider the point 0,0 because it has meaning that is worth discussing.

– When the volume of anything is zero, its mass will be zero, so this is a significant point.

• Toward the end of the Think Aloud, guide students to convert the X-axis units from “number of cubes” to volume.

– Point out that it would be hard to communicate this idea to people who do not know about these particular cubes. It is more useful to state the relationship in universal units, such as cubic centimeters. Students should easily be able to convert the idea of mass per number of cubes to mass/cm3.

– Make this conversion as a class or have a volunteer explain how it is done and mark the change on one of the overhead transparency graphs.

– The calculation is based on an average volume of each cube being between 16.4 and 17.5 cm3. Students can measure the volume of cubes using a caliper or ruler. Some students may have calculated the volume in Step 2.1. You may need to remind students of the formula for the volume of a rectangular solid (V = w x d x h).

Regarding the significance of the slope of the line (representing the density of water or cube combinations comprised of the same type of cubes), consider the following points:

Step 2 Lesson 3: Analyzing Data to Predict What Will Float �9

• If students studied slope as part of their work with force and motion (speed) earlier in the year, then looking at the slope of the line in this example will reinforce those experiences.

• However, if slope has not yet been addressed by students; this in one of those cases when jumping to the technical solution (slope) may be premature and actually unnecessary unless it is a familiar concept or you want to

take time to develop it. All that is needed is to read the value (ratio) of several points on the line, some on the 1, 2, 3, & 4 cubes and some off those whole numbers. The ratio will all be the same. That is all that is needed to introduce density.

5. Revisit the What Makes Things Float? Chart to have the class contribute a new row that represents their learning from this Step 2, so far. It may look like the following example at this point:






prediction?

Measured mass of and floated

cubes

Mass of the cubes and whether they

floated



It is not true that “All wood floats” or “All plastics float”

Measured mass of different cube combinations and

floated them



Measuring mass or weight doesn’t seem to be quite

enough information to always predict correctly whether a group of cubes will float.


It is harder to predict if combinations of cubes will

float than to predict if a single cube will float.

Rate of sinking can be changed by combinations with

different rates of sinking.Plotted data

points on a graph of mass and

volume

For everyone in the class, cubes sank when they were above a certain space on the graph and floated when they

were below it.

There are patterns in the graph of our class data

that may help to predict if something will sink or float

Analyzed plotted data points on

a graph of mass and volume

The mass-to-volume ratio of objects that sink in water is greater than the density of

water.

Measuring and calculating the ratio of mass to volume

for an object makes it easy to predict if the object will sink

or float in water.


6. Direct students to reflect on the list of questions recorded in Step 1, and ask if there are any evidence-based explanations stemming from the work in Step 2 that would help answer any of the questions. Solicit modifications to questions and/or new additions.

7. Use the REAPS questions in Student Page 2.3B: Interpreting Data to check for student understanding of the concept that the mass-to-volume ratio for an object determines whether it floats or sinks in a particular liquid.

Student Page 2.3A: Graphing Results 61

Student Page 2.3A: Graphing Results

0 1 2 3 4 5

number of blocks

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

ma

ss (

gra

ms)

100

Student Page 2.3B: Interpreting Data 6�

The points on this graph represent different tests a student conducted putting the three different types of cubes (A, B, and C) in combinations and floating them in water.

Write your explanations to the following questions on a separate piece of paper.

1. Explain which points on the graph represent Cubes A, B, and C. How do you know?

2. Explain what the density of the water in the beakers must be. How do you know?

3. If you combined one cube of A with one cube of C, would it float? Explain how you know?

4. What did you do to understand what makes things float that was like what scientists do?

Student Page 2.3B: Interpreting Data

Teacher Page 2.3c: Think Aloud Notes for Analyzing Results 6�

Teacher Page 2.3c: Think Aloud Notes for Analyzing Results

--Combine all transparenciesto make singleclass graph to

discuss

--Look for patterns in

data

--Recognize the patternthat sinkers are higher on the

graph than floaters.

--Identify and problem-solve why any data points that don't

make sense might exist as errors.

--Let's look at one group's graph. I'm looking for patterns in their data? Do you see any patterns? Yes, I'm also seeing that all the red dots are toward the top and black dots are closer to the bottom. That's interesting. Do you see any other patterns? (may mention the space with no dots)

--I'm thinking this pattern could mean something important, so I want to see if all the groups' data shows the same pattern. If they do, that tells me the patterns are probably very significant.

--Confirmthe pattern in the data

--Explorethe "space" in the graph

where no data was recorded

--See that sinkers andfloaters are separated by a

space on the graph that could be occupied by a line

with a particular slope.

--Explore ideas for an "object" that would be plotted in that "space."

--I think the separation between sinkers and floaters on this graph is clear enough that I could use this graph to predict if a block would float? Can you see what I mean? What would I measure to use this graph to predict if a block combination would float? (mass and # of blocks)

--I'm thinking this space between sinkers and floater where there is no data is interesting, too! If I did have a cube or group of cubes with the right mass to be plotted in this space, I'm wondering if it would sink or float. What do you think? (float suspended)

--Convertthe X-axis

from"number of cubes" to volume

--Definedensity as the slope of

the line

--See the "space"could be described

by a line with a particular slope: particular to water.

--Recognize density as the slope of the line

describing the mass to volume ratio for a

substance.

--I am wondering how I could measure points on this line in between whole cubes? What if I wanted to measure mass and size of something that wouldn't fit in a cube; how could I plot it on this graph? I'm thinking we need to change the X-

axis to volume. How could I do that? Volume = l x w x h = cm3

--Remember when we used a line to describe speed as a relationship between distance and time? See how this is similar? The slope of this line for comparing mass to volume is particular for water. The slope is a property of water. It is called density. How could I test if other substances would make a line with a slope for density? (test multi-block combinations of the same type of block)

--Confirmthat 1, 2, 3,

or 4 "cubes" of water have a mass in

the "space" and along a

line

--See that sinkersand floaters are

separated by a "space" on the graph that describes water.

--Find that plotted points that represent the mass of a particular amount of

water occur in the "space" onthe graph.

--If a cube or other object would float just beneath the surface of the water, I'm wondering why. How would it compare to water. I'm wondering, if I had a way to put a cube of liquid water in a container of water, would it sink or float? I can't floata cube of water, but I could find out where it would belong on this graph. How could I find out the mass of the amount of water it would take to be the same size as a cube? (calculate"size" of a cube, mass that amount of water)

--I'm curious to try finding the mass of water that would be the size of 1, 2, 3, and 4, cubes and plot that on our graph. (assigngroups to measure --add this data to the graph)

--I see that all the water points we measured and plotted are in the "space" that separates sinkers from floaters. Isn't that interesting! It looks like we could make a line to connect the water data, and that line would separate sinkers and floaters.

Step 2 Lesson 4: Density Defined 67


Key Concepts• Objects with a density less than the

density of water (1 g/cm3) will float in water at some level.


• Scientists seek other sources of information to check their own explanations for accuracy.


• predict if a multi-cube object will sink or float by measuring its density and explaining how that relates to the water in which it will be placed;

• compare the information about density in the student reading to their own understanding of density.


MaterialsFor each student• 1 copy of Student Page 2.4A: What

is Density?

For each group of 4–6 students• 2–3 sets of cubes (Note: Do not refer

to these as “density” cubes with students as their inquiry with the cubes leads to exploration of density)

• 4 large rubber bands• calipers and/or rulers• balances (double balance and/or

graduated or electronic scale)• large container of water in which

cubes can float• towel to clean up spills

Density Defined1. Remind students of the overarching question, What makes things float? and the explanation developed in the previous lesson for the factors that are important to know to predict.

2. Revisit the term density as the class reviews the What Makes Things Float? Chart. Have students calculate and then compare the densities for the individual cubes, using the mass measurements made in Lesson 2.1.

• Use this opportunity to introduce that density is a characteristic property for a pure substance and to emphasize why it is important to measure accurately.

3. Distribute Student Page 2.4A: What is Density? and have students work individually or in pairs to complete the questions that follow the reading.

• Use an appropriate reading strategy to support students’ understanding they key ideas.

• Discuss the questions as a whole class, specifically asking, How did what you read build on what the class learned about density in the previous lesson? and What new information did you learn from the reading?

4. Check for students’ abilities to apply their understanding of density to accurately predict if an object will float, using the class performance task that is outlined in the Implementation Guide.

5. Use a think-pair-share or similar strategy to have students suggest explanations for the Float Demos from Lesson 1.1 based on their understanding of density.

REAPS Questions

The REAPS Questions for this lesson are embedded in the reading and the informal performance assessment task.

Step 2 Lesson 4: Density Defined 69

Implementation Guide1. Remind students of the overarching question, What makes things float? and the explanation developed in the previous lesson for the factors that are important to know to predict. Explain that this lesson has two parts.

In the first part of the lesson, students compare the explanation for the data collected about multiple-cube objects to a reading about the scientific explanation for density.

In the second part, students work together to apply what they know about using evidence to predict if an object will float. This provides an opportunity to check for students’ understanding in preparation for the “Challenge” in Lesson 2.5.

2. Revisit the term density as the class reviews the What Makes Things Float? Chart. Add a new row if students have additional evidence to contribute, and summarize all the evidence that the class now has about the factors that determine if an object will float.

Have students calculate and then compare the densities for the individual cubes, using the mass measurements made in Lesson 2.1.

• Use this opportunity to introduce that density is a characteristic property for a

pure substance and to emphasize why it is important to measure accurately.

3. Explain that in science it is important to assess how well an explanation developed through experimentation aligns with other scientific explanations for the same sort of data. Distribute Student Page 2.4A: What is Density? and have students work individually or in pairs to complete the questions that follow the reading.

• Use an appropriate reading strategy to support students’ understanding they key ideas.

• Discuss the questions as a whole class, specifically asking, How did what you read build on what the class learned about density in the previous lesson? and What new information did you learn from the reading?

– A t-chart (as shown below) on the board to gather students’ responses to these questions can be a useful method for helping students recognize how much of the explanation developed in Lesson 2.3 is supported by additional evidence learned by reading what scientists currently understand about what makes things float.

Statements from the reading that are like what we said in our explanation from Lesson 2.3

New information from the reading about density and what makes things float.


4. Check for students’ abilities to apply their understanding of density to accurately predict if an object will float, using the following performance task.

Begin by having students refer to the What Makes Things Float? Chart to add another row that includes information from the reading and to review what they know about ways to predict if an object will float.

• Use a Think-Pair-Share strategy for students to reason and explain their reasoning as they engage in the interactive demonstration that follows.

a. Make an object from 4 cubes that individually float by connecting them with a rubber band.

b. Record the mass and volume of the object where the class can see the information clearly.

c. Direct students to use what they have learned (and the data in their science notebooks about cube masses) to predict which is the heaviest single cube that could be added to this object without sinking it.

• Have students record their predictions, and have at least one volunteer explain their prediction to the class. Record the cubes predicted by the class, and choose the heaviest to begin testing.

d. After students have recorded their predictions, perform the test. Ask the class, How accurate was your prediction?

e. Ask for a student volunteer to explain for the class, using an overhead projector and Think Aloud, how they calculated and predicted whether the object with cargo would sink or float.

• Students’ reasoning may be something similar to the following: The volume of the object + cargo is volume of 5 cubes or approximately 5 x average volume of a cube. The (mass of object + cargo) / volume must be less than 1 g/cm3 for the object to float. Once students know the mass of object and total volume of 5 cubes, they will know the limit of mass for the cargo cube. For example, a object of 32.5 g including rubber bands will be able to carry a black cube (23.7 g) because the total mass will be 66.2 g (and the volume is 85 cm3), the density will be less than water. This object will sink, however, with the brass-colored cube having a mass of 125.7 g.

f. As you help students with this exercise, keep in mind that it is their ability to recognize the important relationship of density that matters. If their first prediction is wrong, that is OK as long as they go back through their reasoning and calculations and find their mistake. This is not a test but rather an opportunity to clarify what they have discovered in their own open investigation.

5. Use a think-pair-share or similar strategy to have students suggest explanations for the Float Demos from Lesson 1.1 based on their understanding of density.

Student Page 2.4A: What is Density? 71

Like a scientist, you have collected evidence from investigations and used it to develop an explanation about what makes things float or sink. Now, like a scientist, you need to consider what other scientists say about this question and compare it with what you think. Read the article below and think about how it relates to what you did in class.

Different kinds of scientists use density in different ways, but many scientists need to know if specific things will sink or float in water. To determine this, scientists need to know the density of the object, and the density of water. The density of water is the slope of the line on your graph—1. Water weighs 1 gram per every 1 cm3. Why is the density of water 1 gram per cm3?

To answer this question we have to go back in time and travel to France. In 1795, the French government decided to have a standard measure of mass. The French scientists first thought that one liter of water should define this standard measure of mass, and be called a kilogram. There are 1000 milliliters in one liter and there were to be 1000 grams in one kilogram. This meant that one milliliter of water would have a mass of one gram.

Since density is mass per unit volume, this also meant the density of water would be one gram per milliliter, or one gram per cm3.

In the end, the scientists decided not to use water to define the kilogram. Instead, they made a metal block with a mass nearly identical to the mass of one liter of water. The density of water really comes from how scientists a very long time ago decided to define a unit of mass. Fortunately, it is a simple number to remember: 1!

It is important to know the density of water, if you want to know if something will float or sink in water. For example, when you push a block with a volume of 17cm3 under water, you push 17cm3 of water out of the way. Since we know the density of water is 1, 17cm3 of water weighs 17 grams. If the block weighs less than 17 grams, then the block will float. If the block weighs more than 17 grams, then the block will sink.

• Objects that are lighter than the weight of the same volume of water will float.

• Objects that are heavier than the weight of the same volume of water will sink.

Student Page 2.4A: What is Density?

1. Find a partner and answer this question. If an object with a volume of 8 cm3 and mass of 100 grams and was put in water would it sink or float? Why?

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

2. Answer this question on your own. If an object with a volume of 125 cm3 and mass of 50 grams and was put in water would it sink or float? Why?

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

3. How are you behaving like a scientist by comparing the information in this reading to the explanation your class developed for the data in Lesson 2.3?

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

Step 2 Lesson 5: Milestone Challenge #1: Using What We Know about Floating and Sinking 7�


Key Concepts• Objects with a density less than the

density of water (1g/cm3) will float in water at some level.


• complete the Milestone Challenge by correctly calculating and using understanding of the density of the objects, the density of water, and the significance of the density of a solid object relative to the density of water in making a prediction about whether or not it will float.


MaterialsFor each student• 1 copy of Student Page 2.5A: What

Does Density Have To Do With Floating?

For the class• 10 stations with the following

equipment: – calipers and/or rulers – balances (balance beam

scale, triple beam balance or electronic scale)

– container of water in which objects can float

– 1 ping pong ball – the silver-colored cube – rubber band – towel to clean up spills

For the teacher• Teacher Page 2.5a: What Does

Density Have To Do With Floating?

Milestone Challenge #1: Using What We Know about Floating and Sinking1. Distribute to each student a copy of the Student Page 2.5A: What Does Density Have To Do With Floating? Explain that this lesson is one of several “Milestone Challenges” in the Immersion Unit. It is an opportunity to practice using what students understand to predict if a more complicated object than a cube or cube combination will float.

2. Hand out to each student a copy of Student Page 2.5A: What Does Density Have To Do With Floating?

3. Go over the materials, stations, and instructions on the Student Page to prepare students to work individually.

4. After students have completed Student Page 2.5A: What Does Density Have To Do With Floating? and you have assessed their responses, review the questions as a class.

REAPS Questions

The REAPS Questions for this lesson are embedded in Student Page 2.5A: What Does Density Have To Do With Floating?

Step 2 Lesson 5: Milestone Challenge #1: Using What We Know about Floating and Sinking 7�

Advance PreparationIn this lesson, students make a sinker float. They are challenged to predict and explain the behavior of two sets of cubes attached to ping pong balls and placed in a tank of water.

Make certain that students notice that the combination of ball + two black cubes floats higher in the water than does the combination of ball + silver-colored cube.

Set up the materials stations in advance, and position them so that students can work independently. This lesson is intended to provide an opportunity for students and the teacher to assess what individual students have learned and can apply about what makes things float.

Look for student performance on this task to reflect an understanding of density, the density of water, and the significance of density of a solid object relative to the density of water in making a prediction about whether or not it will float.

Even if students make an incorrect prediction initially, their performance ought to be considered a success if after testing they can discover and explain their mistake.


Implementation Guide1. Distribute to each student a copy of the Student Page 2.5A: What Does Density Have To Do With Floating? Explain to students that this is one of several “Milestone Challenges” in the Immersion Unit, and that these challenges are designed to be opportunities for students to apply what they have learned to a particular puzzle.

• This lesson is an opportunity for students to practice using what they understand to predict if a more complicated object than a cube or cube combination will float.

• NOTE: This lesson is a summative assessment opportunity. Plan accordingly to hold individual students accountable if the responses are to be graded.

2. Hand out to each student a copy of Student Page 2.5A: What Does Density Have To Do With Floating?

3. Go over the materials and instructions on the Student Page to prepare students to work individually.

4. After students have completed Student Page 2.5A: What Does Density Have To Do With Floating? and you have assessed their responses, review the questions as a class. The annotated student page provides key teacher notes for each question to help with both grading and post-lesson discussion.

Student Page 2.5A: What Does Density Have To Do With Floating? 77

In your science notebook, record your observations and explanations from this Milestone Challenge. You will make a prediction, test it and explain the results you observe.

1. Which of these objects floats when placed in a tank of water? Find the answer by directly testing each object or combination in a tank of water.

• the silver-colored cube

• a ping pong ball

• the silver-colored cube attached to a ping-pong ball with a rubber band.

Record your observations. Include how much of each floating object is submerged in the water.

Alone, the silver cube sinks. Ping-pong ball floats almost entirely out of the water. Ball attached to cube barely floats. Most of the cube and ball are submerged.

2. The volume of a standard ping-pong ball is 33.5 cm3. Measure the mass in grams (g). You may

need to place a rubber band or other support on the balance or scale to keep the ball from rolling off. Tare before you add the ball. Calculate the density of the ball. How does this information help explain the ball’s behavior alone or attached to the silver-colored cube when they are placed in water? Explain.

3. Alone, black cubes do not float in water. Two black cubes together have a mass greater than that of a single silver-colored cube.

Make a prediction: You carefully attach a ping-pong ball to two black cubes and place them in water. Will the combination float? Write your prediction and your reasoning.

4. When you have completed your answer, test your prediction. How does this combination compare to the behavior of the silver-colored cube attached to the ping-pong ball? Explain the difference.

If you were incorrect, look again at your reasoning and calculations. See if you can find your error. Write a new conclusion. Explain what your error was.

Student Page 2.5A: What Does Density Have To Do With Floating?

Teacher Page 2.5a: What Does Density Have To Do With Floating? 79

In your science notebook, record your observations and explanations from this Milestone Challenge. You will make a prediction, test it and explain the results you observe.

1. Which of these objects floats when placed in a tank of water? Find the answer by directly testing each object or combination in a tank of water.

• the silver-colored cube

• a ping pong ball

• the silver-colored cube attached to a ping-pong ball with a rubber band.

Record your observations. Include how much of each floating object is submerged in the water.

Alone, the silver cube sinks. Ping-pong ball floats almost entirely out of the water. Ball attached to cube barely floats. Most of the cube and ball are submerged.

2. The volume of a standard ping-pong ball is 33.5 cm3. Measure the mass in grams (g). You may need to place a rubber band or other support on the balance or scale to keep the ball from rolling off. Tare before you add the ball. Calculate the density of the ball. How does this information help explain the ball’s behavior alone or attached to the silver-colored cube when they are placed in water? Explain.

Students need to compare total mass (g) to the volume (cm3). If the ratio is greater than 1 g/cm3, it should sink in water. Note that the mass of ping-pong balls varies from 2.1 g to 2.5 g for inexpensive balls. Different brands and grades may have more

Teacher Page 2.5a: What Does Density Have To Do With Floating?

or less variation. Ping-pong balls have an average density of about 0.07 g/ cm3 and thus easily float. Notice that they float very high, with little of the ball submerged.

When the ball is combined with the silver-colored cube, the total mass is about 49 g and the total combined volume is slightly less than 50 cm3 (varies with the ball and rubber band). This just barely floats. Students need to observe how low in the water it floats.

3. Alone, black cubes do not float in water. Two black cubes together have a mass greater than that of a single silver-colored cube.

Make a prediction: You carefully attach a ping-pong ball to two black cubes and place them in water. Will the combination float? Write your prediction and your reasoning.

Although the mass of two black cubes (23.7g + 23.7 g = 47.4 g) is a little more than that of the silver-colored cube (44.1 g), the volume is also greater (there are two cubes). In this case, the combined density is lower, and the combination will float even higher in the water than the single cube-and-ball did.

4. When you have completed your answer, test your prediction. How does this combination compare to the behavior of the silver-colored cube attached to the ping-pong ball? Explain the difference.

If you were incorrect, look again at your reasoning and calculations. See if you can find your error. Write a new conclusion. Explain what your error was.

Step 3 Overview 81

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Overview

The key concept this step covers is that a submerged object displaces a volume of liquid that is equal to the volume of the portion of the object that is submerged.

Students investigate the displacement of a liquid by an object. First, they find a difference in partially submerged (partially floating) versus completely submerged objects. Then, students discover for themselves the relationship between the volume of a submerged solid and the volume of displaced liquid. This lesson’s investigations use water as the liquid, density cubes as the objects, and graduated cylinders to collect quantitative data. Students are guided to conclude that the volume of submerged objects determines how much water is displaced (and that mass is independent of volume).

Step 3 ends with the second Milestone Challenge problem. In this lesson, students are given a classic Archimedes puzzle to solve using the understanding of density and buoyancy that they have developed at this point in the Immersion Unit.

Step 3 Lesson 1: Displacement in a Liquid 8�



Key Concepts• When an object is fully submerged it

displaces a volume of liquid equal to its own volume.

• When an object is partially submerged it displaces a volume of liquid equal to the volume of the portion of the object that is submerged.

• Scientists use multiple methods to calculate volume.


• design and follow a procedure for accurately collecting and measuring the amount of water displaced by an object.

• organize and analyze experimental results to develop an explanation for what determines the amount of water displaced by an object.


MaterialsFor each group of 6 students• 2–3 sets of density cubes • Other small objects that will fit into

graduated cylinders for comparison to density cubes (optional)

• Calipers and/or rulers; balances (double balance and/or graduated or electronic scales)

• 1 beaker• 2 1-Liter graduated cylinders• Towels for cleaning up spills• A few drops of dish-washing detergent

For each student• 1 copy of Student Page 3.1A:

Displacement in a Liquid

For the class• 1 transparency of Teacher Page 3.1a:

Displacement in a Liquid

REAPS QuestionsR What determines how much water an object

displaces? Volume determines how much water is displaced, provided gravity or some other external force is sufficient to at least partially submerge the object.

E If an object is floating or partially submerged what volume of water does it displace? Whatever volume of object is under water is the volume of water that is displaced.

A When would it be logical to measure volume with the displacement method rather than direct measurement? If the object has an irregular shape it might be difficult to directly measure the dimensions of the object.

P What do you predict will happen if you placed the cubes in liquid oil or orange juice? Would the same amount of liquid be displaced as in water? Students may not be prepared at this point to recognize that the density of the liquid affects the buoyancy of the object. This question is posed to provide an opportunity to learn about students’ prior knowledge and current perceptions of buoyancy.

S What decisions and changes did you make as you planned the procedure to use to run tests helped you make more accurate measurements?

Displacement in a Liquid1. Begin Lesson 3.1 with a quick review of the Question Wall, and highlight any questions in which the floating object in question is an irregular shape (difficult to measure the volume). Follow up with a description of the Milestone Challenge that students will solve in the next lesson, using what is learned in Lesson 3.1.

2. Assign students to groups of 6 who will share an Equipment Station. Explain that students will work in pairs or groups of three to complete the Student Pages; however, groups are encouraged to collaborate in gathering and analyzing evidence.


3. Distribute Student Page 3.1A: Displacement in a Liquid to each student, and have students work in pairs to review the instructions. Review the key points as a class, and highlight the two questions posed:

• What can you measure to predict how much water is pushed out of the way, or displaced when an object is placed in a liquid?

• Does whether an object is fully or partially submerged make a difference to how much water is pushed out of the way by the object?

4. Show students the materials that are provided for use in their investigations and provide a time limit.

• Review how to measure water volume with a graduated cylinder.

5. Guide a whole-class discussion about students’ responses to the Student Page questions and analyzing the results to develop explanations for the questions.

6. Work as a class to contribute a new row to the What Makes Things Float? Chart.


Step 3 Lesson 1: Displacement in a Liquid 8�

Advance PreparationRead the Question Wall questions before beginning this lesson to identify any student-generated questions that could possibly require measuring the volume of an irregular object to gather evidence for an explanation. If there are no such questions, then you can provide one.

Gather materials for the Equipment Stations in advance. Keep in mind that it is critical that students gather all water that overflows and measure it with a graduated cylinder to have results that can be correctly interpreted. Collecting the displaced water will be easier if you apply a drop or two of dishwashing detergent (soap) to the water. This reduces surface tension and should make it easier to top-off the container and more accurately measure the volume of displaced water. There will probably be an error of about 2 mL in measuring the volume which is perfectly acceptable for this experiment, and for comparing this data to others later in this unit.


Implementation Guide1. Refer students to the Question Wall as this lesson begins and point out any questions that could require measuring the volume of an irregular object to gather evidence for an explanation. If there were no such questions, then suggest an additional question for the Wall that involves calculating like the density of an irregular object. For example,

• Suggest a scenario in which a man owns a beautiful piece of metal jewelry and becomes suspicious that it has been stolen and replaced by a replica made of a much cheaper metal.

• How might understanding density make it possible to determine if he still has the original? How could he determine the density of the piece of jewelry if it is an irregular shape whose volume cannot be easily measured?

Allow students to share their ideas about the answers to these questions and how they would go about collecting evidence to answer them. Remind students that the best explanations are supported with plenty of evidence. Explain that today, they will be collecting evidence that may help them explain these kinds of questions.

Highlight any questions on the question wall that involve objects floating at different levels in the water like “Why do some blocks float right near the surface and others float deeper in the water?” Tie back to the Step 2 investigations by asking, What is the significance of the fact that floating objects may sit at different levels (different degrees of submersion) in the liquid?

Share that in the next lesson the will face another Milestone Challenge that will require the knowledge and skills they will learn in this lesson. In the next Milestone Challenge a 1st place and 2nd place medal for a sporting event are mixed up. They will need to determine which medal is which using their knowledge of density.

2. Divide the class into groups of 6 students who will share an equipment station. Explain that students will work individually to complete procedures and questions on the Student Page that they will receive. However, encourage collaboration within and among groups to gather and analyze evidence.

3. Distribute the Lesson 3.1 Student Page: Displacement in a Liquid—one for each student. Have students work in pairs to review the instructions. Review the key points as a class, and highlight the two questions posed:


• Does whether an object is fully or partially submerged make a difference to how much water is pushed out of the way by the object?

4. Familiarize students with the materials available for their investigations.

• Remind students how to read the meniscus to determine the volume of water in a graduated cylinder. (The curved surface of the liquid is called a meniscus. As a standard procedure, always read the level of the liquid at the bottom of the curve.)

• Designate a specific amount of time for students to conduct investigations. You may wish to begin with 40 minutes and then check in with groups to see if additional minutes are needed.

5. Bring students back together as a whole class and gather responses to the Student Page questions.

• Call upon students to diagram on an overhead what they did to gather evidence to answer the questions.

• Have students use a “Think Aloud” method to explain their reasoning.

Step 3 Lesson 1: Displacement in a Liquid 87

• Intervene with short explanations and probing questions to clarify the key evidence supporting the concepts that

– When an object is fully submerged, it displaces a volume of liquid equal to its own volume.

– When an object is partially submerged it displaces a volume of liquid equal to the volume of the portion of the object that is submerged.

Observed and measured the

amount of “overflow” fluid

from the container


Objects that sink raise the fluid level in their container

Not sure. Volume is related to density but it alone cannot be used to predict whether an

object floats.One way to find the volume of an irregularly–shaped object is to measure the volume of

fluid it displaces

6. Add another row to the What Makes Things Float? Chart and any new questions to the Question Wall. The new row for the chart might include entries like the chart below.


Student Page 3.1A: Displacement in a Liquid 89

Student Page 3.1A: Displacement in a Liquid

1. Can you recall a time when you dropped an ice cube into a glass of water or soda and had the glass overflow? Maybe you’ve filled a sink with water to do dishes and had it nearly overflow when you added the dishes. The water that was pushed out of the way when you added the ice cube to your drink or the dishes to the full sink is called displaced water. What causes the water to be displaced?

1A. What can you measure that would allow you to predict how much water will be displaced when an object is fully submerged in a liquid (when an object is fully submerged it is completely beneath the surface)?

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1B. How would the amount of displaced water be different if the object was only partially submerged (for example, a floating cube that is half-way beneath the surface)?

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2. Work with a partner to build on the following procedure to design an experiment to test for evidence that can explain answers to the questions being asked.

• Fill a container with water.

• Determine what type of object(s) you need for the experiment.

• Record the mass and volume of the objects.

• Place each object in the container of water, and figure out a procedure to measure how much water it displaces.

Plan carefully—How will you measure ACCURATELY how much water an object displaces? Imagine this situation and how you could collect and measure the water that overflows:

A tub of water is filled to the brim with water. As soon as any object touches the surface, some water spills over the side. Once the object is in the water and settles down, some amount of water has overflowed. That is displaced water. That is the water you want to measure! How can you measure it?

Think about how to carefully collect and accurately measure the overflow, EVEN IF IT IS A TINY AMOUNT. How have you measured the volume of liquids before? Plan with your partner the procedure you will use.

Student Page 3.1A: Displacement in a Liquid 91

Student Page 3.1A: Displacement in a Liquid (continued)

3. Use your experimental procedure to collect evidence in Experiments A, B, and C. For each of these experiments, create an object from the cube combination, measure its mass, calculate its volume, and use your procedure to measure how much water it displaces. In Experiment C, the cubes will be only partially submerged. Record your data in the chart below.

Experiment A

Object 1 Description: 1 copper and 1 aluminum cube

Object 2 Description: 1 brass and 3 nylon cubes

Experiment B

Object 3 Description: 1 copper and 1 aluminum cube

Object 4 Description: 2 nylon cubes

Experiment C

Object 5 Description: 2 pine cubes and 2 oak cubes

Record how much of Object 5 is below the surface of the water.

Lesson 3.1 Data Chart

Experiment A Experiment B Experiment C

Object 1 Object 2 Object 3 Object 4 Object 5

Calculated volume of object (mL)

Measured volume of displaced water (mL)

Mass of object (g)

Fully or Partially Submerged (F or P)

Other observations

NOTE: Keep this table and data for use in Lesson 4.2

Student Page 3.1A: Displacement in a Liquid 9�

Student Page 3.1A: Displacement in a Liquid (continued)

5. In Experiment A, what observations or measurements did you make that were close to the same for Object 1 and Object 2? Which were different?

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6. In Experiment B, what observations or measurements did you make that were close to the same for Object 1 and Object 2? Which were different?

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7. In Experiment C, what determined whether the object would sink or float?

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8. Which object in Experiments A and B were similar to the Object in Experiment C? Explain all the similarities that you observed.

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9. Think about what the evidence you collected tells you about displacement. What can you measure to predict how much water is pushed out of the way, or displaced when an object is placed in a liquid?

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10. Does it make a difference how much water is pushed out of the way if the object is fully or partially submerged?

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Teacher Page 3.1a: Displacement in a Liquid 9�

Experiment A Experiment B Experiment C

Object 1 Object 2 Object 3 Object 4 Object 5

Calculated volume of object (mL)

Measured volume of displaced water (mL)

Mass of object (g)

Fully or Partially Submerged (F or P)

Other observations

NOTE: Keep this table and data for use in Lesson 4.2

Teacher Page 3.1a: Displacement in a Liquid

Step 3 Lesson 2: Milestone Challenge #2—Which Medal? 97


Key Concepts• When an object is fully submerged,

it displaces a volume of liquid equal to its own volume.



• outline a method for making measurements and using density to determine a solution to the problem presented in Milestone Challenge #2—Which Medal?



Milestone Challenge #2 – Which Medal?

Milestone Challenge #2—Which Medal?1. Guide the class to reflect on the What Makes Things Float? Chart, and ask students to contribute any additional questions to The Question Wall that they have at this point. Review what students now know about what determines whether something will float.

• Ask students to reflect on what understanding displacement affects their ability to predict what floats (it is a way to measure volume, and that must be measured to determine density).

2. Divide the class into groups of two students. Explain that this Milestone Challenge is an opportunity to apply their understanding of density to a scenario that could happen in real life.

3. Give each student a copy of Student Page3.2A: Milestone Challenge #2 – Which Medal?

• Explain the amount of time students will have to complete the challenge (20 minutes recommended)

4. Read the problem in the challenge, and check for students’ understandings of what is expected.

5. Provide time for students to complete the challenge in pairs.

6. Conduct a whole-class discussion of the Milestone Challenge question.

REAPS Questions

The REAPS Questions are embedded in Student Page 3.2A: Milestone Challenge #2 – Which Medal?

Step 3 Lesson 2: Milestone Challenge #2—Which Medal? 99

Implementation Guide1. Guide the class to reflect on the What Makes Things Float? Chart, and ask students to contribute any additional questions to The Question Wall that they have at this point. Review what students now know about what determines whether something will float.

Ask students to reflect on what understanding displacement affects their ability to predict what floats (it is a way to measure volume, and that must be measured to determine density).

Focus the whole-class introductory discussion to remind students what they learned in the last lesson and explain that this will be important in solving the Milestone Challenge puzzle. Emphasize that students will be working in groups (2 students per group), and the goal is for each group to develop the best possible evidence-based explanation for a solution to the problem.

2. Assign partners and explain how you expect groups to work. Emphasize that both students are responsible for being prepared to explain their solution to the challenge problem.

3. Provide students with their own copy of Student Page 3.2A: Milestone Challenge #2 – Which Medal?

• Explain the amount of time students will have to complete the challenge (20 minutes recommended)

4. Read aloud or use another strategy to be certain that all students understand the problem presented in the Milestone Challenge and know their options for responding.

• Suggest that partners, if they prefer, can draw a diagram with captions to explain their answer. Provide large paper for that option so that both students can work on the drawing.

5. Start the time for completing the challenge. While students work, circulate among partners and encourage students to use evidence from previous lessons to explain their solutions.

6. Conduct a whole-class discussion of the Milestone Challenge question. Have students with various approaches to explaining their solution present their work to the class. As they present, as them to be explicit about their reasoning when developing their solution.

Student Page 3.2A: Milestone Challenge #2—Which Medal? 101

Rodney and his friend Mark just finished competing in the national skate boarding championships held in Seattle, Washington. For their outstanding performances, Rodney earned 1st place and received a platinum medal. Mark received a sterling silver medal for 2nd place. The medals were nearly identical. Each had a carving of a skateboarder and the Seattle skyline etched into one side, and the year and national championship logo on the other. They were even the same color. The only difference was the type of metal used to make them.

After the awards ceremony, Mark and Rodney left their medals on a table and raced off to skate together one last time. They needed to hurry because Rodney had to catch a plane home. After their skate, Rodney quickly grabbed a medal and rushed to the airport.

When Rodney arrived home, he was very proud of his victory and immediately showed his medal to his friends. He told stories of the new tricks and grinds he had learned from the competition. As Rodney was admiring his medal and thinking back on how he had won by only a few points, he remembered the victory skating he did with Mark. Suddenly, he thought the medal felt different than it

had in Seattle. He began to wonder if he had picked up his platinum medal from the

table or, if by accident, he had picked up Mark’s silver medal.

Rodney went to his computer and found a Web site that gave information about platinum and sterling silver. The site said that a platinum ring could cost as much as two hundred times the price of a silver ring. This made Rodney even more concerned that he may have picked up the wrong medal. He really needed to figure out if he had

the right medal.

With your partner, come up with a plan to help Rodney decide if he has the correct medal. You can choose between two options for explaining what he needs to do.

Option 1) Write a detailed explanation.

Option 2) Create a poster with any number of pictures or symbols, but only 5 words.

For whichever option you choose, you must explain:

• all the evidence he would need to collect;

• how Rodney should collect that evidence, including any equipment he would need to use and how he should use it.

Student Page 3.2A: Milestone Challenge #2—Which Medal?

Step 4 Overview 10�

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Overview: Buoyancy and Forces

The key concepts this step focuses on include:

• Gravity pulls down on all objects.

• There is an observable difference in the forces that act on an object that is in air versus water.

• The buoyant force pushes up on all objects and depends on the submerged volume of the object.

• Buoyancy is determined by differences between the gravitational force and the buoyant force.

• Changing the weight or the volume of an object can affect buoyancy.

Step 4 guides students to develop an understanding of key factors related to buoyancy as follows:

Lesson 4.1: Students investigate on their own the forces on an object submerged in liquid (a heavy object lifted out of water). They review their understanding of forces and find that whether something floats depends on a balance of gravity and an upward force, later termed the buoyant force.

Lesson 4.2: Students quantify the balance of forces involved in buoyancy. They use a spring scale and experiment with objects that float or sink in water. Students find that the loss in apparent weight of a submerged object is proportional to its volume (and the volume of displaced water).

Lesson 4.3: In a demonstration investigation, students apply their understanding of density and buoyancy to boats and find that the mass/volume ratio determines if an object will float in water. Then, in Milestone Challenge #3, students apply their understanding of buoyancy to predict the maximum payload that a small boat made from a bottle cap can carry.

Step 4 Lesson 1: Exploring Apparent Weight 10�



Key Concepts• Gravity pulls down on all

objects.• There is an observable difference

in the forces that act on an object that is in air versus water.

• Water exerts an upward force on objects.


• construct diagrams of forces, including the direction and relative strength of forces, acting on objects in air and water, showing that water exerts an upward force on objects.



Drawing Forces• 1 copy of Student Page 4.1B:

Archimedes Investigations

For the class• 1 10-gallon aquarium or other

clear tank, large enough for a class demonstration

• 1 rock, brick, or other heavy object for demonstration that will fit in the tank

• 1 water-tight plastic container (like Tupperware™) with a lid that fits in the demonstration tank

• 1 or more rubber bands strong enough to lift the heavy object

• 1 overhead transparency of Teacher Page 4.1a: Drawing Forces

REAPS QuestionsR Where do objects feel heavier, in the air or in the

water? Objects feel heavier in air.E What seems to cause the difference in how heavy

objects feel in air versus water? What the object is in (air or water) is what seems to determine the difference in forces acting on the object.

A Is the upward force greater on a rock sitting on a table in air than for a rock sitting in an aquarium full of water? Explain your answer. The upward force is greater on the rock in the aquarium full of water because the rock feels lighter in water. Something has to be pushing up against its weight to make it feel this way.

P Do you think that the differences in the forces acting on an object are the same for an object between air and water as they are for an object between air and oil? Answers may vary. Accept all responses at this point. This question probes students’ thinking about the upward forces apparent in other liquids, besides water.

S What is one thing you find challenging about drawing diagrams of forces? What strategy will you use to help yourself overcome this challenge? Students may suggest drawing the forces in the correct direction or with the correct relative strengths.

Exploring Apparent Weight1. Refer to the Question Wall and highlight questions relating to the buoyant force, however, do not refer to it as “buoyant force” since that term has not been introduced yet.

2. Conduct the rock-in-water demonstration with rubber bands. Give several students the opportunity to feel the difference in the weight of the rock and share their experiences with the class.

3. Give a brief introduction (or review) of how to draw arrows (vectors) of different lengths to represent forces acting on an object.


4. Distribute Student Page 4.1A: Drawing Forces. Direct students to draw arrows on the rock in air and the rock in water, as they perceive them.

• Stress that these are initial ideas and there will be additional opportunities to modify these drawings as more evidence is collected.

5. Bring the class together and ask several student volunteers to reproduce the arrows drawn on their Student Page on a larger drawing that the whole class can see.

• Before having students do this part, draw the heavy object in air and water in advance so that student volunteers can simultaneously and quickly add the arrows.

6. Use a Think Aloud strategy to show how you interpret the arrows that students drew in terms of the forces on objects. Check with the students who drew those arrows to see if your interpretation is what they intended to communicate.

• NOTE: Stress that these drawings represent INITIAL ideas that students have about the forces acting on the rock, and explain that the class will be gathering evidence over the next two lessons to understand the forces.

• Use Science Notebooks and a class discussion to talk about and record where the rock (or other heavy object) feels heavier (in air or water). Continue having students explore this phenomenon by introducing a plastic container that can be pushed into the demonstration tank to feel the difference in force needed to submerge it a little (partially submerged) compared to submerging it a lot (fully submerged at different depths).

– Again, have several volunteer students demonstrate pushing on the plastic container and describe the experience to the class.

7. Use Science Notebooks and a class discussion to talk about and record where the rock (or other heavy objects) feels heavier (in air or water). Continue having students explore this phenomenon by introducing a plastic container that can be pushed into the demonstration tank to feel the difference in force need.

8. In their Science Notebooks and on Student Page 4.1A: Drawing Forces, have students record their observations.

– Allow students to come to the demonstration tank and make direct observations while the class is recording notes.

9. Use Teacher Page 4.1a: Drawing Forces and facilitate a whole-class discussion to draw one diagram that correctly reflects the relative strengths of forces acting on the heavy object in air and in water. During this guided discussion, clarify the following key points:

• The upward force on an object that is exerted by water is greater than the upward force on an object that is exerted by air.

• The upward force on an object that is fully submerged is greater than the upward force on an object that is partially submerged.

10. Explain that Student Page 4.1B: Archimedes Investigations includes a story that is often told (and students may have heard) for comparison to their experimental results. Assign the reading using an appropriate reading strategy, and discuss in light of the explanations the class developed from their experiments.


Step 4 Lesson 1: Exploring Apparent Weight 107

Teacher Background Information

force pushes back against gravity to make it float. Therefore, trying to fully submerge something like a Tupperware container (closed and filled with air) into water will require some force to counteract that upward force from the water. The force required to push the container into the water as it is partially submerged increases gradually until it reaches a maximum when it is just fully submerged, just below the surface of the water. Then, no matter how deep the container is pushed, one will feel the same amount of “push-back” from the water trying to keep the container afloat.

Advance PreparationSetup the clear demonstration tank with water ahead of time and have a heavy object (like a rock or brick) ready for students to test.

In this lesson, students can notice that heavy objects are noticeably less heavy when placed in water. This illustrates the concept of apparent weight. Apparent weight is how much an object seems to weigh, even though its true or real weight may be heavier. When any object is placed in water, the water exerts an upward force on the object (which scientists call the buoyant force). This upward force opposes the downward force of gravity and makes the object feel less heavy, giving it a lower apparent weight compared to when it is in air.

In the same way, one can feel that floating objects are hard to submerge. The upward (buoyant)


Implementation Guide1. Remind students of the Question Wall, and point out any questions that relate to the buoyant force such as, “What holds things up when they float?” This is the focus of Lesson 4.1: The idea of an upward force on an object in water is introduced here, and by the end of Lesson 4.1 students ought to be consciously aware of the apparent weight change for an object in air versus water. The term “buoyant force” will be attached to students’ understanding in the next lesson. For now, use other terms (like “upward force”) to refer to the buoyant force.

2. Take a rock or other large, heavy object and lift it up off the ground or table. Describe how heavy it feels. Then, place the rock in the clear tank of water and describe how its weight feels different. The change in forces can be more easily felt if one or more rubber bands are attached to the object and it is raised and lowered into and out of the water by holding the rubber band.

Allow several students the opportunity to experience this difference in apparent weight and let them also describe their experience to the class while holding the heavy object with the rubber band in and out of water.

3. Briefly introduce (or review, if previously taught) how to draw arrows (vectors) of different lengths to represent forces acting on an object. Be sure to emphasize that the length of the arrows represents the relative strength of the force.

4. Distribute Student Page 4.1A: Drawing Forces to focus attention on how to represent forces on paper. Direct students to draw arrows on the rock in air and the rock in water. Remind students to draw the arrows to represent the forces they felt from the heavy object in the demonstration. Whatever was perceived in the demonstration is what should be represented with arrows.

• Stress that these are initial ideas and there will be additional opportunities to modify these drawings as more evidence is collected.

5. Bring the class together and ask several student volunteers to reproduce the arrows drawn on their Student Page on a larger drawing that the whole class can see. The idea is to have volunteers from each group briefly sketch and explain their thinking.

• Before having students do this part, draw the rocks in air and water in advance so that student volunteers can simultaneously and quickly add the arrows. This could be done on chart paper or a chalkboard, for example.

6. Use a Think Aloud strategy to show how you interpret the arrows that students drew in terms of the forces on objects. Check with the students who drew those arrows to see if your interpretation is what they intended to communicate. The Think Aloud could sound something like the following:

On this diagram of a rock sitting on a table, surrounded by air, I see two arrows were drawn. From what I know about forces and motion, since the rock is not moving, the arrows must represent forces that are equal in strength and point in opposite directions.

I remember the saying, “the sum of forces must equal zero when an object is at rest.” So this one, pointing down, represents the object’s weight, due to gravity. And this one, pointing up, represents the normal force from the table, opposing gravity. [To student: Is that what you were thinking?]

OK, now in this diagram where the same object is sitting at the bottom of a tank of water, I see three arrows. This one looks the same as before—it points down and represents gravity. [To student: Is that right?]

This one looks almost the same as before – it also points up and comes from the table on which the tank is resting, but it is a little shorter. [To student: Does this represent the normal force?]

Well, if that is the normal force, then I see one other force, also pointing up and that one is new. I wonder if it has something to do with the water since that is the only thing that changed when the rock was moved from the table to the tank.

Step 4 Lesson 1: Exploring Apparent Weight 109

• NOTE: Stress that these drawings represent INITIAL ideas that students have about the forces acting on the rock, and explain that the class will be gathering evidence over the next two lessons to understand the forces.

7. Use Science Notebooks and a class discussion to talk about and record where the rock (or other heavy objects) feels heavier (in air or water). Continue having students explore this phenomenon by introducing a plastic container that can be pushed into the demonstration tank to feel the difference in force needed to submerge it a little (partially submerged) compared to submerging it a lot (fully submerged at different depths).

• Again, have several volunteer students demonstrate pushing on the plastic container and describe the experience to the class.

8. In their Science Notebooks and on Student Page 4.1A: Drawing Forces, have students record their observations and questions about their observations.

• Allow students to come to the demonstration tank and make direct observations while the class is recording notes.

9. Use an overhead transparency of Teacher Page 4.1a: Drawing Forces to facilitate a whole-class discussion about the forces everyone felt with the heavy object demonstration. Draw one diagram that correctly reflects the relative strengths of forces acting on the rock in air and the rock in water. During this guided discussion, clarify the following key points:

• The upward force on an object that is exerted by water is greater than the upward force on an object that is exerted by air.

• The upward force on an object that is fully submerged is greater than the upward force on an object that is partially submerged.

• In their Science Notebooks and on Student Page 4.1A: Drawing Forces, have students record the class’s consensus for how to draw the forces exerted on the rubber-banded rock in air and in water.

– Provide students with time to discuss with their partners the class’s representation of the forces exerted on the rock.

10. Explain that Student Page 4.1B: Archimedes Investigations includes a story that is often told (and students may have heard) for comparison to their experimental results. Assign the reading using an appropriate reading strategy, and discuss in light of the explanations the class developed from their experiments.


Student Page 4.1A: Drawing Forces 111

Student Page 4.1A: Drawing Forces

1. Draw what you think the forces are on the rock when it is in air (suspended by a rubber band).

Remember, the length of an arrow represents the amount of force. Arrows of the same length represent forces of the same strength. Arrows of different lengths represent forces of different strengths.

2. Now, draw what you think the forces are on the rock when it in water (suspended by a rubber band).

Student Page 4.1A: Drawing Forces 11�

Student Page 4.1A: Drawing Forces (continued)

3. Draw what the class decided the forces are on the object in the tank:

4. Next, draw what the class decided the forces are on the object in the tank:

5. Talk with your partner about the following questions:

• Do you agree with what the class decided the forces are on the rock in water and in air? Why or why not?

Did you have to change the length of the arrows between the object in the tank and the object in air? If so, what could make the strength of the forces different for the object in the tank compared to the object in air?

Student Page 4.1B: Archimedes Investigations 11�

Archimedes performed many experiments with water and he investigated floating and sinking objects. He proved important things about what makes objects float. His work was so important that there are even legends about it. One legend goes something like this:

Some time around 265 BCE, Hiero II, the king of Syracuse, gave a goldsmith a lump of gold and asked him to make a crown out of it. The goldsmith made a beautiful crown, but the king noticed that it seemed to be a different color than the lump of gold had been. He wondered if perhaps some silver had been mixed in with the gold. He weighed the crown and it weighed exactly the same as the lump of gold he had given the goldsmith. King Hiero was satisfied that he had gotten back all his gold, but

the scientist Archimedes was not so sure. He, too, thought the crown’s color was different. Archimedes told the king that just because the crown weighed the same as the lump of gold, that didn’t mean that it was pure gold. It could still have silver, or some other, less valuable, metal in it.

Hiero challenged the scientist to figure out if the goldsmith had indeed cheated him, but warned Archimedes not to damage the crown. Archimedes did not know how to tell if the crown was all gold, or part gold and part silver, but he said he would begin some experiments. He thought and thought about the problem. One day he stepped into a very full bathtub to rest and think about the crown. Some water spilled out, and he got an idea. He thought if a smaller man had gotten into the tub, less water would have overflowed.

Student Page 4.1B: Archimedes Investigations

Archimedes: mathematician, engineer, patriotic Greek

• Lived: ca. 287 BCE to ca. 212 BCE

• Birthplace: Syracuse, Sicily

• Famous Quote: “Eureka!” meaning “I have found it”

More than two thousand years ago, a great scientist named Archimedes investigated questions that interested him and his country. His research lead to many important discoveries in math and science. He figured out the value of pi (π), and that the volume of a sphere was 4/3πr3. He also invented many important machines like Archimedes Screw, which allowed people to lift water up out of rivers and lakes for drinking and irrigating fields. We still use this invention today in places like this

wastewater treatment plant in El Paso, TX.

Image courtesy of Parkhill, Smith & Cooper, Inc., Geof Harral, and the El Paso Water Utilities


Student Page 4.1B: Archimedes Investigations 117

He jumped from the tub and ran naked down the streets yelling “Eureka! Eureka!” which in English means “I have found it! I have found it!” Archimedes knew that a pound of silver was bigger than a pound of gold. If the crown had silver in it, the crown would have a bigger volume than a lump of pure gold of the same weight. All he had to do was figure out the volume of the crown and the volume of the same weight of pure gold.

He took a lump of gold the same weight as the crown and determined its volume by submerging it in water. Then, he determined the volume of the crown by submerging it in water. The crown had a larger volume than the lump of pure gold! This proved that the goldsmith had taken some of the gold and used a less a dense metal in its place. The crown was a fake, the thief was likely punished, and Archimedes discovered an important idea in science…or so the story goes.

This is just a legend, and since these things happened a very long time ago nobody is really sure of the

Student Page 4.1B: Archimedes Investigations (continued)

details. However, the story can still tell us something about the history of how scientists investigated density and something about density itself.

How does the investigation that Archimedes similar to what you did to answer the following questions?


• Does it make a difference how much water is pushed out of the way if the object is fully or partially submerged?

• What can you measure that would allow you to predict how much water will be displaced when an object is fully submerged in a liquid?

• How would the amount of displaced water be different if the object was only partially submerged?

Teacher Page 4.1a: Forces 119

Teacher Page 4.1a: Forces

Step 4 Lesson 2: A Balance of Forces 121



Key Concepts• Buoyancy is determined by differences

between the gravitational force and the buoyant force.


• explain that the gravitational force an object experiences is relative to an object’s mass, not its volume, and that the buoyant force is relative to an object’s submerged volume

• design and conduct an investigation that helps them explain buoyancy in terms of gravitational and buoyant forces.


MaterialsFor each student:• 1 copy of Student Page 4.2A:

A Balance of Forces• 1 copy of Student Page 4.2B:

Remembering Archimedes

For each group of 6 students• Ping-pong balls• 1 set of density cubes• 3 large rubber bands• Large clear container for water• 3 spring scales (spring balance)• Calipers and/or rulers• 1–3 graduated cylinders

For the class• 1 transparency of Teacher Page 4.2A:

A Balance of Forces

A Balance of Forces1. Refer students to the What Makes Things Float? Chart and discuss what observations and evidence from Lesson 4.1 could be added to the chart. Wrap up the discussion by explaining that the problem posed in this lesson is to figure out a way to make an object sink that would otherwise float.

2. Prepare students to work with a partner within a group of six who will share materials. Show students the materials provided for investigations in this lesson.

3. Provide each student with a copy of Student Page 4.2A: A Balance of Forces. Remind students of the observations made in Lesson 4.1, and explain that in this lesson the questions are:

• How can you measure the forces that are exerted on an object in air and in water.

• Are the forces the same in air and in water?

4. Circulate among groups as they work on the challenges posed by Student Page 4.2A: A Balance of Forces. Ask probing questions and prompt students to look for patterns in their results that would explain how the forces act on floaters and sinkers.

5. Check for students’ understandings while discussing as a class Student Page 4.2A: A Balance of Forces. Use a Think Aloud script for how to guide students through the process of looking through and analyzing data.

6. Distribute Student Page 4.2B: Remembering Archimedes and have students read the short article to introduce the scientific term buoyant force.

7. Again, direct students to add a row to the What Makes Things Float? Chart and discuss what evidence was gathered and explained in this lesson that was left unanswered from Lesson 4.1.



REAPS QuestionsR What keeps floating blocks from sinking? The balance

of upward force (buoyant force) and downward force (gravitational force) is such that there is more upward force, so the cube does not sink.

E Explain whether cubes with the same volume have the same downward force exerted upon them. Not necessarily. Downward force is dependant on the objects mass. So two cubes with the same volume would only have the same downward force due to gravity if the had the same mass.

A Explain whether or not cubes with the same volume have the same upward force exerted upon them? Cubes of equal volume have the same upward buoyant force exerted on them if they were both fully submerged. If they floated at different levels in the water, the buoyant force would be different on each cube.

P How can you predict the amount of weight that a boat could carry without sinking? Once the buoyancy of the boat is determined by calculating its density, and if the density of the liquid is known (salt or fresh water), then the amount of mass that can be added can be calculated. The mass can only be increased so that the density of the boat with its load is less than the density of the water.

S How did keeping detailed records in your science notebooks help you with the work you did today, and what improvements could you make to the way you keep your science notebook to make it more useful? Students may refer to being able to look back at diagrams for forces from the last lesson and their thinking and data for the Milestone Challenge #1.

Step 4 Lesson 2: A Balance of Forces 12�

Teacher Background InformationIn this lesson, students conduct a quantitative study of the forces at work when an object is lowered into a tank of water. In this step, students are following up on the question raised at the end of Step 1: How can you investigate the relationship between gravitational force, a force pushing back when an object is submerged, and the displaced volume? They use a spring scale and discover that:

• the apparent weight of an object goes to zero if the object floats,

• if an object sinks, when it is submerged the apparent weight is reduced, and

• the apparent loss of weight is constant once the object is completely submerged, regardless of how far it is below the surface.

Through experimentation, students find that the apparent weight is reduced by an amount numerically equal to the volume of water displaced by the submerged object. Finally, they recognize that buoyancy is a balance of forces: gravitational force and buoyant force.

• The gravitational force on an object on Earth is determined by the mass of the object.

The buoyant force on an object is determined by its volume and the density of the liquid in which it is submerged.

To gather evidence about forces, students attach a spring scale (sometimes called a spring balance) to an object and record its apparent weight in air. Most scales record weight in the standard units of force, Newtons. Some balances, such as the one pictured here, record weight in grams. Explain to students the relationship between mass and weight. The gram measure will be easier to use when comparing

displaced volume, but students should not think that it is a direct measurement of weight (force). A scale that displays units of grams will tend to blur the distinction between mass (measured in kilograms or grams) and force (measured in Newtons). However, it makes the correspondence between the volume and buoyant force more obvious (at least for objects in water under Earth’s normal gravitational pull). This is simply because the mass of one milliliter (volume) of water is 1 gram.

Observations can be made in air, with an object partially submerged and fully submerged. Students will compare the changes in apparent weight (whether measured in Newtons or grams).

Observation for a cube that sinks:

Reading with cube in air

Students compare the apparent weight in air and water for several objects (such as the density cubes) that all sink. If the volume is constant, and the sinking behavior is the same, the only variable will be apparent weight: students will discover that regardless of the total value, the increment of change is the same if the cubes are fully submerged.

Reading with cube in water


Implementation Guide1. Begin the lesson by referring students to the What Makes Things Float? Chart and discussing what evidence was gathered in Lesson 4.1 that can be added to the chart.

• Wrap up the discussion by explaining that the problem posed in this lesson is to figure out a way to make an object sink that would otherwise float.

The entry for the chart after Lesson 4.1 may look something like the following:





prediction?

Felt the forces on a heavy, sinking

object and a light, floating object in air

and water

Qualitative measurements of forces

Floating objects “push back” with a force due

to the water

Heavy objects appear less heavy in water

Not sure. Knowing the amount of “push-back” force may help predict if an object

will float.

2. Prepare students to work with a partner within a group of six who will share materials. Show students the materials provided for investigations in this lesson.

3. Provide each student with a copy of Student Page 4.2A: A Balance of Forces. Remind students of the observations made in Lesson 4.1, and explain that in this lesson the questions are:

• How can you measure the forces that are exerted on an object in air and in water.

• Are the forces the same in air and in water?

4. Circulate among groups as they work on the challenges posed by Student Page 4.2A: A Balance of Forces. Pose questions to help students analyze their results and develop explanations. Look for students’ initial observations to be similar to the following:

• apparent weight is reduced when the object is submerged

• change continues until the object is fully submerged, but additional depth does not result in additional reduction of apparent weight

• amount of change is the same for any of the cubes of same volume, regardless of the total apparent weight or mass. In other words, an object of mass 137 g undergoes the same apparent change when submerged as does an object of 20 g if the volume is the same.

• apparent weight goes to zero when the object is floating.

• amount of reduction in apparent weight for floating objects matches the volume of the submerged part of the object.

Note: Some students may think that gravity affects only the cubes that sink. Make certain that they understand that all cubes are pulled down by gravity. The floaters simply have a different balance of gravitational and buoyant force.

Step 4 Lesson 2: A Balance of Forces 12�

5. When students have completed their investigations, review Student Page 4.2A and results as a class.

• From the work that students do in the Student Page and the whole-class discussion of their results, guide students to understand that Buoyancy is determined by a difference between the gravitational force and the buoyant force.

• Make the connection between density and buoyancy.

– Density determines if an object will sink or float in a particular liquid. Whatever portion of the object is submerged (below the surface) determines how

much liquid is displaced. The weight of the liquid displaced is the buoyant force. So, the volume of an object that is submerged is directly related to the buoyant force on the object.

6. Distribute Student Page 4.2B: Remembering Archimedes and have students read the short article to introduce the scientific term buoyant force.

7. Again, direct students to add a row to the What Makes Things Float? Chart and discuss what evidence was gathered and explained in this lesson that was left unanswered in Lesson 4.1. Point out how quantifying measurements helped build a more complete explanation.

The additional row may look something like this:





prediction?

Used a spring scale to measure the weight of objects in water and

air


Sinking objects must have an upward force on

them that makes them appear to weigh less in

water than in air

Different liquids and gases seem to “push back” in

different ways.

Objects that sink weigh less in water than they

do in air


Student Page 4.2A: A Balance of Forces 127

Student Page 4.2A: A Balance of Forces

• How can you measure the forces that are exerted on an object in air and in water. Are the forces the same?

How to Measure ForcesA spring scale is a tool used for measuring force. When you use a spring scale to measure the weight of an object, you are really measuring the force exerted by the object onto a spring. The object’s weight pulls it down and the spring, when it is extended, pulls up against gravity until the object rests at some level. The weight of the object and the force inside the extended spring are equal and act in opposite directions. This is an example of balanced forces.

Part A: Measuring Weight:

1. Predict and Record: Which object do you think would generate a greater downward force (gravitational force) on the spring scale –– a floater or a sinker?

2. Figure Out: Design a plan for testing your prediction in #1. Draw a diagram of your design, and explain your procedures.

3. Observe and Record: Try your experimental plan from #2, and record observations below.

4. Analyze: Does the evidence from your experiment support your prediction from #1?

Part B: Measuring Apparent Weight in Air vs. Water

1. Predict and Record: For any of the cubes, how will the apparent weight in air compare with the apparent weight in water?


Student Page 4.2A: A Balance of Forces 129

Student Page 4.2A: A Balance of Forces (continued)

3. Observe and Record: Use the same cube combinations that you used in Lesson 3.1—and try your experimental plan from #2. Record your observations in the following table. Also, transfer the data about the amount of displaced water that you recorded for each cube combination in Lesson 3.1?

Cube combinations from Lesson

3.1

Floater or Sinker?

Apparent Weight in Air

Apparent Weight in

Water

Change in Apparent Weight

Water displaced

(from Lesson 3.1)

4. Analyze:

a. Look back to Lesson 3.1 (Displacement of Liquids). In the table you used in #3, make a notation about how much water was displaced by each of the cubes.

b. What is the connection between the amount of change in apparent weight and the amount of water displaced by a cube?

Part C: Testing Different Volumes

1. Predict and Record: How will increasing the volume of a cube affect the change in apparent weight between air and water?


3. Observe and Record: Create a data table to record your observations. Include a column in your data table to record observations about the change in water level for each trial.

4. Analyze: Explain the data from your experiment.

5. Making Connections: Look back at your observations in Milestone Challenge #1. Recall what happens to a silver-colored cube + ping pong ball and two black cubes + ping-pong ball in water.

Use what you have learned about the balance of forces in buoyancy. Explain why these objects both float but at different levels.

1�0 Buoyancy and Density: What Makes Things Float?

Student Page 4.2B: Remembering Archimedes 1�1

Remember Archimedes, the famous Greek scientist that discovered a way to measure the volume of irregularly shaped objects? He thought of this technique of measuring volume when he got into a very full bathtub and some water spilled over the side.

The volume of the water that spilled onto the floor was equal to his body’s volume. He used his idea to check to see if King Hiero’s crown was pure gold and had some less dense silver mixed in with it. If it was a fake and had silver in it, it would have a larger volume than the same weight of

pure gold.

When Archimedes climbed into that bathtub, he also noticed something else that was even more important to science than a new way to measure volume. Archimedes noticed that he felt lighter when he got in the tub. Archimedes discovered that the water was pushing on him.

It was opposing some of his weight.

He called this force that the water was exerting the buoyant force. The amount of the buoyant force was related to the volume of water that had been displaced when he got into the tub. In fact, the buoyant force is equal to the weight of the displaced fluid.

This statement became known as Archimedes’ Principle. It is an important piece of understanding for engineers who build boats, hot air balloons, submarines, air ships, and other floating objects.

Student Page 4.2B: Remembering Archimedes

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1�� Buoyancy and Density: What Makes Things Float?

Step 4 Lesson 3: Predicting Payload 1��


Key Concepts• Materials more dense than the

liquid they are submerged in can still float, just use balance of forces in design


• explain that boats can float in water so long as the overall density of the boat is less than the density of water

• calculate the maximum amount of payload a boat can carry based on the mass and volume of the boat.



Milestone Challenge #3—Predicting Payload

For each group 4–6 students• Container of water• Pennies or other small objects for

payload• Towel to clean up spills

For the class• Modeling clay (enough to

make a cube for a whole-class demonstration)

• 1 large container of water for the demonstration

Predicting Payload 1. Begin the lesson with a brief discussion about boats and what students know about different boat shapes and materials.

2. Ask, What determines how much weight a boat can carry? Guide the discussion to incorporate what students know about boats with the facts that:

• the whole volume of the boat determines the upper limit on how much water can be displaced

• empty boats displace less volume than loaded boats

3. Conduct a demonstration inquiry with clay to reinforce the idea that changing the volume of an object changes its density and buoyancy.

4. Direct students to review the evidence and understandings the class has been recording in the What Makes Things Float? Chart. Use this discussion to review what students already know about measuring the volume of an object and how boats present a slightly different challenge for measuring volume.

5. Give each student a copy of Student Page 4.3A: Milestone Challenge #3—Predicting Payload.

• Read through the instructions and check for understanding.

6. Allow students approximately 30 minutes to complete the Challenge.

• NOTE: This is NOT to be a trial-and-error exercise.

7. After all students have completed the Milestone Challenge and received individual feedback from you and/or through peer review, discuss the challenge, results, and key concept:

• The whole volume of the boat determines the upper limit on how much water can be displaced. Empty boats displace less volume the loaded boats.



REAPS QuestionsR In order for your boat to float what does the overall

density of the boat and its contents need to be less than? It needs to be less than the density of water or 1g/cm3.

E Will two boats of the same size with different numbers of pennies in them displace the same amount of water? No the boat with more pennies would float lower in the water, displacing more water.

A If one boat displaces more water than another does, which one has more buoyant force being exerted on it? The one that displaces more water. The buoyant force is equal to the weight of the displaced water.

P How would you need to adjust your maximum payload if the boat was to float in liquid oil instead of water? Students should justify their prediction either way. For example, “I predict that it would carry more pennies because I think oil is more dense than water” or “I predict it would carry less pennies because oil is less dense than water.” Use this to determine what students know about the different densities of liquids before beginning Step 5.

S Explain what would you change about your investigation or prediction if you were able to conduct this challenge again. Students may cite that they needed to have predicted one less penny than their calculations show due to instability in the boat or that they needed to have standardized the way they added pennies to the boat to prevent it from tipping prematurely.

Step 4 Lesson 3: Predicting Payload 1�7

Teacher Background InformationAfter a brief demonstration about how changing the volume of an object changes its density and buoyancy, in this Milestone Challenge, students build simple boat (from foil or bottle cap), make measurements and predict how many pennies it will carry. Then they test their prediction and explain the results.

For simplicity and uniformity among students, we recommend that you use flat plastic bottle caps such as those from gallon jugs of water or smaller plastic water or soda bottles. You may want to give students two different size caps to test, or you might want to let them try on one size, analyze their results, correct errors in reasoning or measurement, then repeat the test with a larger cap and grade the result.

Note that the uneven rim of this bottle cap on right side is actually below water level but held up by surface tension. Shaving or sanding the edge of cap smooth can avoid this complication. Adding a little bit of liquid soap to the water may also help.

The bottle caps are useful because the rigid, flat shape is fairly stable and the caps are not expensive. Pennies provide a convenient payload because they provide small increments of mass (about 2.5g/penny) and are flat and will lay on bottom of boat, adding to stability. Provide a variety of bottle caps so that no two students working near each other are likely to have the same volume cap. Consider having students bring bottle caps to class.

One difficulty to watch for is that some caps have a slightly uneven or serrated edge that interacts with surface tension of water and results in a boat barely floating with larger than the theoretical payload limit. You can minimize this effect by shaving or sanding the edge of the cap. A smooth edge behaves in a more predictable manner. Alternatively, let students compare caps with smooth or rough edge so they recognize the effects of surface tension.

We recommend that you pre-measure and test the caps and pennies before the student performance task. If you prefer to have students calculate the cap volumes, they may need help making the calculations. Remind them that the volume is the area of the bottom (π r2) multiplied by the height of the cap. Point out that measuring the diameter is easier than measuring the radius. Some caps are knurled to provide a better grip. This can make the determination of an exact value for the effective diameter slightly tricky. Alternatively, you can calculate the volumes of the caps and provide that information to increase the likelihood that it will be an accurate measurement.

You may need to remind students that the meaningful volume is that of the boat as a container. In other words, they need to determine the volume of the plastic and its interior space, not the volume occupied by the plastic alone.


Advance PreparationVerify that the clay you are using has a density such that it does not float. Prepare a tank of water for the clay boat demonstration.

Plan how you will provide students access to water to test their predicted payloads in the Milestone Challenge.

Examples:

Small cap: A plastic cap from a small water bottle has a diameter of 2.9cm and height of 1.1cm. We divided by 2 to get a radius of 1.45cm. The area of the bottom is:

• r2 = 1.45cm x 1.45 cm x 3.14 = 6.59cm2

• Volume = area of base x height = 7.2 cm3

This is the outer volume, but that is what determines the mass of payload it will carry. The total mass of the loaded boat (boat + payload) cannot exceed 7.2 g.

We found the mass of the cap to be 1.5 g. The difference between this value and the potential total mass is 5.7 g, the largest payload the boat can carry. Dividing this number by the average mass of pennies (2.5g), we predicted the boat would carry 2 pennies but sink with 3 pennies. Our test showed this prediction to be correct.

To test the prediction, we pre-loaded the boat with pennies laid flat on the bottom and then carefully slipped the boat-cap into the water. It is necessary to prevent pennies from sliding and to avoid tipping water into the boat when launching it. A hand placed under the boat as it is laid onto the water’s surface is helpful.

Large cap: A cap of diameter is 5cm and height 1.3cm has a volume of 24.1 cm3. Its mass is 3.9 g. Maximum predicted payload is 20.2 g or 8 pennies. We found this prediction correct except when surface tension on uneven edge barely supported a boat with 9 pennies. Surface tension effectively had increased the height of the boat. You might ask students if they would like to depend on a boat that used surface tension to avoid sinking when they got into the boat!

(continued on followiong page)

Step 4 Lesson 3: Predicting Payload 1�9

Summary Table for Sample Caps

Large Small

Diameter 5.0 cm 2.9 cm

Radius (calculated) 2.5 cm 1.45cm

Height 1.3 cm 1.1 cm

Volume (π r2 x height) 24.1 cm3

7.2cm3

Mass 3.9 g 1.5 g

Maximum predicted payload 20.2 g 5.7 g

Predicted # pennies(mass of max payload /mass of penny)

8 pennies

2 pennies

(continued from previous page)


Implementation Guide1. Introduce Lesson 4.3 with a class discussion about boats. Ask students what they know about boat shapes and the materials they are made from. Probe for ideas like:

• boats can have different shapes

• boats can be a solid object like a raft

• boats can be a container with an interior space. (Note: When it is a container, the volume is bigger than just the material the boat is made of).

2. Ask, What determines how much weight a boat can carry? Guide the discussion to incorporate what students know about boats with the fact that the whole volume of the boat determines the upper limit on how much water can be displaced. Empty boats displace less volume than loaded boats.

3. Conduct a demonstration inquiry with clay to reinforce the idea that changing the volume of an object changes its density and buoyancy.

• Hold up a clay cube, and show that it sinks. Ask students if there is a way that this clay could be made to float. Ask back to students with ideas for making it float what evidence they have that their idea will work.

• If a student recommends that you flatten the clay and provides a well-reasoned explanation why you should, do so. If no students suggest flattening the clay, ask students to predict what they think will happen if you do.

• When this amount of clay is flattened (shaped into a boat), it floats. Ask students, Has the density of the clay itself changed? No, the clay has the same density even when it is divided into parts. (Remember from previous activity?)

• Ask students to explain why the clay boat floats. Guide the discussion to focus on the key points that:

– When the clay is flattened, it has the same mass but greater volume.

– The mass determines the downward force (due to gravity).

– The submerged volume determines the upward force.

– The boat has more than enough potential upward force to balance the downward force, so it floats.

• Ask the class, What determines the mass of payload the boat will carry?

• Guide the discussion for students to recognize that the excess of potential upward force (beyond that needed to balance the mass of the boat) determines how much payload the boat will carry.

4. Direct students to review the evidence and understandings the class has been recording in the What Makes Things Float? Chart. Use this discussion to review what students already know about measuring the volume of an object and how boats present a slightly different challenge for measuring volume.

5. Give each student a copy of Lesson 4.3 Student Page: Milestone Challenge #3—Predicting Payload.

• Read through the instructions and check for understanding.

6. Allow students approximately 30 minutes to complete the Challenge. Check with students as they work to be sure they record their predictions and methods for making the predictions. This is NOT to be a trial-and-error exercise.

7. After all students have completed the Milestone Challenge and received individual feedback from you and/or through peer review, discuss the challenge, results, and key concept:

• The whole volume of the boat determines the upper limit on how much water can be displaced. Empty boats displace less volume than loaded boats.


Student Page 4.3A: Milestone Challenge #3—Predicting Payload 1�1

How will you USE EVIDENCE to PREDICT what a small “boat” can carry and still float?

1. Show your reasoning, measurements, and calculations for determining the largest possible payload of pennies that your assigned boat can carry.

THIS IS NOT “TRIAL AND ERROR” TEST. You must show how you calculate the recommended payload for the boat. Then launch your boat to test your prediction.

Remember: the more pennies your boat carries, the more valuable the payload. But if you predict more than it will carry, the boat will sink. You lose your payload and your boat!

Hints for success:

• Show your reasoning, measurements and calculations.

• Measure mass of pennies you use. Do not assume all pennies are the same.

• Make the edge of the boat smooth. This gives a uniform surface. Otherwise, the surface tension of the water may make the boat behave in an unpredictable way.

2. Test your prediction, and explain your results.

• Place the payload in your boat before the boat is in the water. If you add a penny, remove the boat first, add the penny and then put it back in the water.

• Remember: If your payload is off-center, your boat will tilt. It may take on water and sink.

• When you launch the boat, place it in the water very gently. Be careful to avoid tipping.

3. Explain how the forces acting on your boat affect the outcome. In your explanation, include a diagram with arrows representing the forces.

Student Page 4.3A: Milestone Challenge #3—Predicting Payload

Step 5 Overview 1��

S T E P

�

Overview: Fluids and Buoyancy

The key concepts this step focuses on include:

• The density of liquids affects the buoyancy of objects submerged in those liquids.


• The principles of density apply to gases in addition to liquids and affect the buoyancy of objects in those gases.

This step addresses the question of whether or not the fluid is a factor in what makes things float. Students must transfer what they have learned about solids to a new situation where the liquid (or gas) is considered in more detail. Differences in density of fluids based on composition or temperature are uncovered in a student-directed investigation. The second lesson includes an intriguing story about what happens when gas and liquid are mixed in an unusual circumstance.

Step 5 Lesson 1: Liquids and Buoyancy 1��


Key Concepts• The density of liquids affects the

buoyancy of objects submerged in those liquids.



• recognize that liquids can have different densities.

• design an experiment in which the density of liquid affects the results.


MaterialsFor the class

For a class of 30 students• 30 copies of Student Page 5.1A:

Liquids and Buoyancy (distributed AFTER the investigation)

For teacher-led demonstration:• Heat source for water• Source of ice• Very small slide-lock plastic bags

For each group of 4–6 students• 1 set of density cubes and optional

other small objects that float• containers for water (preferably

acrylic tank to hold several cubes at one time)

• pipettes• triple beam or electronic balance• saturated salt water• concentrated (90% solution or

greater) isopropyl alcohol• safety goggles (and gloves,

optional)

Liquids and Buoyancy1. Perform three demonstrations in front of the class to pique interest in density of liquids and how it is affected by temperature (see Implementation Guide).

• Have students contribute to a class list their questions that arise from the demonstrations.

2. Help refine student questions and provide them with materials to work in groups of 4–6 for their own investigation of liquids and density.

3. Form student-groups of four to six who are interested in a similar question or questions chosen by the class.

• In their science notebooks, have students record both their question and prediction with an explanation for what the answer may be.

4. Use an appropriate strategy to check the appropriateness of students’ experimental designs before having them begin their independent investigations on liquids and density.

5. Before students analyze their results, remind them of the graph made for sinker and floater solids (cubes and cube combinations from Step 2) and ask, “Could a graph predict whether a liquid can float on another liquid?”

6. Have students briefly report their observations to the class.

7. After a whole-class discussion, distribute Student Page 5.1A: Liquids and Buoyancy. Instruct students to write responses to the questions in their science notebooks.

8. Complete this lesson by having students add a row to the What Makes Things Float? Chart and discussing the REAPS questions.


REAPS QuestionsR Give an example of one liquid on which oil floats

and one in which it sinks. Oil floats on water and sinks in isopropyl alcohol.

E Describe how the plot of mass and volume of liquids is like the plot of floating cube combinations you made in Step 2. Both plots show a relationship between mass and volume that we call density. Both show the values of density that objects must have in order to float or sink.

A Look at the table of densities of common materials that your teacher provides. Use the table and what you learned about density and floating to explain to someone why the statement “all wood floats” is not true. Can you name a material in which some wood sinks? If so, which material and which kinds of wood?

P What would someone need to know in order to predict whether an object could float in a mixture of liquids and gases? It would help to know the density of the mixture, or the densities of the gases and liquids that make up that mixture and how much of them there are in the mixture.

S Discuss the Predict question with a partner and make a list of things you would need to know to answer that question.

Step 5 Lesson 1: Liquids and Buoyancy 1�7

Teacher Background InformationKnowing the density of the fluid is just as important as knowing the density of the object in that fluid in order to determine whether it will sink or float. Until this point in the Immersion Unit, the fluid has mainly been water. It is important to remember that all fluids (liquids and gases) have density and this includes liquids other than water. A plot of mass versus density for liquids will look similar to the

plot of mass versus density for solids as was made in Step 2. The principles of density and buoyancy for solids remain the same for liquids. Things may look different since liquids, unlike solids, do not have precise shapes, but the ideas of density and buoyancy determining what makes one liquid float or sink in another are the same.


Advance PreparationFor the three demonstrations, the following materials can be prepared in advance. NOTE: As an alternative to performing the demonstrations, a video clip is provided on this unit’s CD showing an oil drop in the alcohol/water layered interface. There is no audio, so you can describe what is shown as you watch the video with your class. It shows what is described in Demonstration 2 below.

Demonstration 1: Prepare two beakers full of water. One should be a saturated solution of salt water. (Use rock salt to prepare this solution if you want it to be clear.) Test the plastic density cubes in the beakers before class to make certain that the salt water is concentrated enough. Both plastic cubes should sink in plain water, but in salt water, as shown below, the white (Nylon) cube floats while the clear (Acrylic) cube sinks.

Demonstration 2: In a transparent container (preferably tall and narrow), carefully layer alcohol on top of water. It is recommended you use a 90% solution of isopropyl alcohol (or more concentrated, if possible) because the difference in density between it and pure water is high enough for it to separate easily. (91% should be available at a local drug store, if not through a chemistry lab or supply company). A drop of vegetable oil, when placed gently on top of the alcohol will sink through it and rest on the interface between the alcohol and water as represented in the line drawing below.

WARNING: Isopropyl alcohol is NOT the alcohol found in beverages. Drinking it is dangerous and can make a person very sick. Warn students NOT TO DRINK OR TASTE IT.

Demonstration 3: Prepare containers of hot and ice-cold water. Fill two small zip-lock bags with water (one hot, one cold). Be sure to squeeze any air bubbles out of the bag as much as possible before sealing. When these bags are placed in containers of water with the opposite temperature, you should notice the cold water bag sinking (in hot water) and the hot water bag rising (in cold water). This demonstration illustrates the effect of temperature on the density of a liquid.

Step 5 Lesson 1: Liquids and Buoyancy 1�9

Implementation Guide1. Introduce the lesson by asking, “Does the liquid make a difference in what makes things float?” Then perform three demonstrations.

• Drop a pair of plastic density cubes in each beaker of water (one plain and one saturated with salt). Ask students to record what they observe and to begin thinking about how to investigate the behavior of the cubes.

• Allow one student to gently place a drop of cooking oil on top of the liquid in the narrow container full of water and alcohol. Ask students to speculate about what could be happening and tell them they will have an opportunity to investigate.

• Place small bags of hot and cold water in containers of water with the opposite temperature. Allow students to observe what happens to the bags of hot and cold water in their respective containers. Ask students to draw conclusions about how temperature affects density based on their observations.

Have students contribute to a class list their questions that arise from the demonstrations.

2. Have students refine their questions to specific variables or concepts. They might ask:

• Do different liquids have different densities?

• Is the density of salt water greater than that of water?

• Does the density of a liquid affect the way a solid object floats or sinks in it?

• Could a liquid of lower density float on top of a more dense liquid?

• What other differences in liquids could affect the way things float?

Use a similar process as used in Step 1 to refine some of the questions to be testable with the available materials.

3. Form student-groups of four to six who are interested in a similar question or questions chosen by the class.

• In their science notebooks, have students record both their question and prediction with an explanation for what the answer may be.

4. Use an appropriate strategy to check the appropriateness of students’ experimental designs before having them begin their independent investigations on liquids and density.

• Students can compare and contrast the densities of water, saturated salt water and alcohol through careful measurement.

• They can collect evidence directly by measuring the mass of a known volume of each liquid and calculating the density.

• Students might try layering alcohol on water or salt water and repeating the oil droplet test. Alternatively, they could add some food coloring to water and try the layering to see if one liquid floats on another. Because students also are investigating how the surrounding liquid affects the way a solid floats, they could test objects that are nearly neutral (by constructing combinations of ping pong balls and cubes or by using other plastics) to see if the behavior is different in hot or cold water or in regular or salt water. They could also experiment with sugar-water.

5. Before students analyze their results, remind them of the graph made for sinker and floater solids (cubes and cube combinations from Step 2) and ask, “Could a graph predict whether a liquid can float on another liquid?” Students can measure the mass per volume (in milliliters) of the three liquids. Using pipettes, they can add one mL at a time to a container on a scale and record the mass with each increment. Pipetting must be done carefully. If students repeat measurements or pool and average their data, the results are likely to be more accurate.

Because of problems with viscosity and subsequent inaccurate measurements, it is suggested that students NOT measure small amounts of oil. They can measure the density based on a larger volume or you could supply this figure (to avoid using lots


of oil). Vegetable oil has a density of about 0.9 g/cm3. The density for different vegetable oils varies slightly.

Guide students to organize their evidence into a graph, as they did in Step 2

6. Have students briefly report their observations to the class.

• Students may have observed a linear relationship of mass to volume and that different liquids have different densities.

• Students can make an analogy to the density graph and recognize that salt water would sink under pure, fresh water and alcohol would float on either one. Students may also

recognize that hot water is less dense than cold water.

• Ask for applications to everyday life.

7. After a whole-class discussion, distribute Student Page 5.1A: Liquids and Buoyancy. Instruct students to write responses to the questions in their science notebooks. Answers are provided on the corresponding Teacher Page 5.1a. In addition, the Analyze REAPS question requires the table of densities found on Teacher Page 5.1b.

8. Complete this lesson by having students add a row to the What Makes Things Float? Chart and discussing the REAPS questions. For this lesson, the chart entry might look something like the following:





prediction?

Observed oil and water together in one container

Oil floats in water Liquids can have different densities, not

just solids

Measuring the density of a liquid helps predict if it

will float on another liquid.

Analyzed plotted data points on a graph of

mass and volume (density)

Liquids can have different densities, not

just solids

If you are working with a pure liquid (or solid or

gas), it is possible to know what the density is by

looking it up or measuring it just once, because it is a property that stays the

same for a pure substance.

The mass-to-volume ratio of liquids that float (or sink) in other liquids is greater than (or less than) the m/V ratio of

the other liquids

Student Page 5.1A: Liquids and Buoyancy 1�1

After you have investigated the density of liquids and how that affects buoyancy, respond to these questions in your science notebook. In each case, explain your answers using evidence from your investigation.

1. What force pulls down on the liquids?

2. What force pushes back on alcohol layered on water and keeps the alcohol on top?

3. Why does the oil droplet stop at the interface between alcohol and water?

4. Explain what forces cause the white plastic cube to float in saturated salt water but sink in fresh water.

5. Work with a partner to solve the following problem:

Student Page 5.1A: Liquids and Buoyancy

Teacher Page 5.1a: Liquids and Buoyancy 1��

Teacher Page 5.1a: Liquids and Buoyancy

After you have investigated the density of liquids and how that affects buoyancy, respond to these questions in your science notebook. In each case, explain your answers using evidence from your investigation.

1. What force pulls down on the liquids?

Gravity.

2. What force pushes back on alcohol layered on water and keeps the alcohol on top?

Buoyant force. Since water is more dense than alcohol, it provides the buoyant force that supports the layer of alcohol.

3. Why does the oil droplet stop at the interface between alcohol and water?

Vegetable oil is more dense than alcohol but less dense than water, so it sinks in alcohol and floats in water.

4. Explain what forces cause the white plastic cube to float in saturated salt water but sink in water.

In both cases, gravity pulls down on the cube by the same amount. If submerged, the cube displaces a volume of liquid equal to the volume of the portion of the cube that is submerged. This volume of salt water has more mass than the same volume of pure, fresh water. (Salt water is more dense than pure, fresh water.) For this reason, salt water exerts a greater buoyant force on the cube. The buoyant force of the salt water is enough to balance the downward gravitational force. The cube floats in the salt water. The buoyant force of the pure, fresh water is not enough to balance the downward force, so the cube sinks in regular water.

5. Work with a partner to solve the following problem:

According to the given data, the layers will be as follows:

Layer 1 = water, Layer 2 = crude oil, Layer 3 = octane (a component of gasoline)

Teacher Page 5.1b: Density Table 1��

Teacher Page 5.1b: Density Table

Densities of Common Materials(at room temperature unless otherwise noted)

Material Density (g/cm3)

Balsa wood 0.11–0.14

Cork 0.22–0.26

White pine wood 0.35–0.50

Oak wood 0.60–0.90

Hexane 0.65

Cardboard 0.69

Octane 0.70

Ethanol 0.78

Ice 0.917

Crude oil* 0.79–0.97

Olive oil* 0.80–0.92

Water (4 °C) 1.0

Asphalt 1.1–1.5

Ebony wood 1.11–1.33

Brick 1.4–2.2

Sugar 1.59

Bone 1.7–2.0

Sandstone 2.14–2.36

Granite 2.64–2.76

Diamond 3.51

Cast iron 7.0–7.4

Stainless steel 7.8

Bronze 8.74–8.89

Data adapted from the CRC Handbook of Chemistry and Physics, 86th Edition, CRC Press, Boca Raton, FL, 2005–6 except where noted with an asterisk (*). Asterisk data adapted from SI Metric, Internet: http://www.simetric.co.uk/si_liquids.htm.

Step 5 Lesson 2: Gases and Buoyancy 1�7


Key Concepts• The principles of density apply

to gases in addition to liquids and affects the buoyancy of objects in those gases.


• correctly explain a plausible explanation for the story in Student Page 5.2A: Gases In the Ocean.


MaterialsFor each student• 1 copy of Student Page 5.2A: Gases

In The Ocean

Gases and Buoyancy1. Refer to the Question Wall and What Makes Things Float? Chart, and conduct a brief discussion about density and gases. Ask for students’ common experiences with the density of gases.

2. Distribute Student Page 5.2A: Gases in the Ocean and read the story as a class.

3. Instruct students to form groups of 3-4 and answer the Think and Write questions at the bottom of the student page.

4. Conduct a whole-class discussion about the questions to check for understanding.

5. Work as a class to contribute a new row to the What Makes Things Float? Chart.

REAPS Questions

REAPS Questions are embedded in Student Page 5.2A: Gases In The Ocean

Step 5 Lesson 2: Gases and Buoyancy 1�9

Teacher Background InformationLarge methane gas deposits exist beneath parts of the ocean floor, especially in the North Sea where a lot of oil is also found. Organic matter in the ocean floor sediment can generate methane over long periods of time. Sometimes these methane deposits break free and form gas bubbles in the ocean. As the bubbles travel up through the water towards the surface, they lower the average density of the water. (Gas is much less dense than water.) Thus, anything floating on the surface above this column of bubble-filled water could sink since the water underneath is no longer as dense (buoyant) as it once was.

Scientists hypothesize that these methane bubbles are the cause of some shipwrecks. Indeed one ship from the early 1900s was found lying flat on the ocean floor within a region known to contain methane deposits.

Scientists have confirmed this idea by collecting data from small-scale experiments and computer models.

Sources of information for the Gases In The Ocean story:

“Can a single bubble sink a ship?”

D.A. May and J.J. Monaghan, Am. J. Phys. 71, 842, 2003.

“When do bubbles cause a floating body to sink?”

B. Denardo, L. Pringle, C. DeGrace, and M. McGuire, Am. J. Phys. 69, 1064, 2001.

“Monsters of the Deep”

J. Marchant, New Scientist, Issue 2267, 20–21, December 2, 2000.


Implementation Guide1. Refer to the Question Wall to see if any questions refer to the density of gases. Inform students that gases have density just like liquids and solids and this can affect the buoyancy of objects in the gas. Ask students to think of some examples of objects that depend on the density of gases to float. (Some common examples include hot air balloons and helium balloons.)

Compare the key factors that determine what floats in a gas to the evidence for predicting if an object will float in a liquid on the What Makes Things Float? Chart. The chart at this point may look similar to the following example.





prediction?






plastics float”Measured mass of different cube combinations and

floated them



Measuring mass or weight doesn’t seem to be quite enough

information to always predict correctly whether

a group of cubes will float.

Not sure. We need to know more to always make accurate

predictions.

It is harder to predict if combinations of cubes

will float than to predict if a single cube will

float.Rate of sinking can be changed because cube combinations sink at

different rates.Plotted data points on a graph of mass

and volume

For everyone in the class, cubes sank when

they were above a certain space on the

graph and floated when they were below it.

There are patterns in the graph of our class data

that may help to predict if something will sink or float

Step 5 Lesson 2: Gases and Buoyancy 161

Analyzed plotted data points on a

graph of mass and volume

The mass-to-volume ratio of objects that sink in water is greater than

the density of water.

Measuring and calculating the ratio of mass to volume

for an object makes it easy to predict if the object will sink

or float in water.Observed and

measured the amount of “overflow” fluid from the container


Objects that sink raise the fluid level in their

container

Not sure. Volume is related to density but it alone cannot be used to predict whether an

object floats.One way to find the volume of an irregularly-

shaped object is to measure the volume of

fluid it displacesFelt the forces needed to sink

floating cubes and ping-pong balls

Qualitative measurement of forces

Ping-pong balls “push back” with a greater

force than floating cubes when you hold them

under water.

Not sure. Knowing the amount of “push-back” force may help predict if an object

will float.

Used a spring scale to measure the

weight of objects in water and air


Sinking objects must have an upward force on

them that makes them appear to weigh less in

water than in air

Different liquids and gases seem to “push back” in

different ways.

Objects that sink weigh less in water than they

do in airObserved objects

floating on the surface of liquids

Whether objects float or sink in liquids

There is a balance of forces on floating

objects

Not sure. The liquid has something to do with whether

objects float.Floating objects remain at rest where they float

Observed oil and water together in one

container

Oil floats in water Liquids can have different densities, not

just solids

Measuring the density of a liquid helps predict if it will

float on another liquid.Analyzed plotted data points on a

graph of mass and volume (density)

Liquids can have different densities, not

just solids

If you are working with a pure liquid (or solid or gas), it is possible to know what the density is by looking it

up or measuring it just once, because it is a property that

stays the same for a pure substance.

The mass-to-volume ratio of liquids that float (or sink) in other liquids is greater than (or less than) the m/V ratio of

the other liquids


2. Distribute the Student Pages for this lesson and read the story as a class.

3. Allow students to form groups of 3-4 and take out their science notebooks. Ask students to work on the Think and Write questions at the end of the Student Page as a group. Remind them that they can use evidence from the rest of the unit, including any notes from their science notebooks, to answer the questions and discuss them as a group.

4. When the majority of groups are nearly finished with the Think and Write questions, bring the class back together for a whole-class discussion. Review students’ answers for the Think and Write questions and be sure that students are supporting their

explanations with evidence from data they have seen or collected during the unit.

• Probe students’ depth of knowledge with questions like: How do you know?

This whole-class discussion is also an opportunity to identify any lingering misconceptions or misunderstandings about density and buoyancy. The next step is the final, evaluation step for this unit.

5. Add another row to the What Makes Things Float? Chart and any new questions to the Question Wall. The new row for the chart might include entries like the following:

Read a story about methane gas in the

ocean

The density of gases like methane and air

Gases can have different densities too!

Gases that are less dense than the fluid they are in will

always float. Gas bubbles rise in liquids

Student Page 5.2A: Gases in the Ocean 16�

Imagine working for a fishing company. Each day you would load up the boat with fishing gear, maps, and other supplies. You would head out to sea and spend the day catching fish to sell on the mainland. Some days you would catch many fish, the sun would shine, and the ocean would be calm. Other days things might not go so well. What might a really bad day on a fishing boat be like?

Fishing all day and not catching anything? Losing your nets? Being out all day in rain and rough waves? None of those things would make for a nice day at sea, but worst of all might be the boat, without warning, sinking like a stone to the bottom of the ocean. Truly, a fishing company’s worst nightmare!

Luckily for fishing boats it does not happen very often, but there are many tales of boats sinking without warning, especially in particular parts of the ocean. The Witches Ground in the North Sea between Scotland and Norway is one area that has a reputation for sinking ships. Scientists sent a remote controlled submarine down to one of the sunken vessels to help determine what caused it to sink. They found it sitting upright, telling them it was not the result of a hole in the hull or being swamped by large waves. What else might have caused an otherwise seaworthy boat to sink like a stone?

This question intrigued scientists from all around the world. Australian scientists David May and Joseph Monaghan studied the Witches Hole area extensively. They conducted surveys of the ocean floor around the sunken boat looking for anything that seemed unusual. They discovered that the boat was right in the middle of what appeared to be a large crater, and all around it were methane hydrate deposits.

May and Monaghan knew that methane hydrate deposits were evidence that methane gas was

Student Page 5.2A: Gases in the Ocean

under the ocean floor. Other scientists had already discovered that methane gas is released from decomposing organic matter deep underneath the ocean. The gas works it way upwards to the ocean floor, and under the enormous pressure of the ocean water it does not escape. Instead, it can form methane hydrate deposits.

Based on their observations and the work of other scientists, May and Monaghan made an important prediction. They predicted that if the methane hydrate deposits were disturbed, the methane gas below them could escape. This would create bubbles at the surface, possibly very large bubbles, which could have sunk the ship. They had two key pieces of evidence for their prediction. The crater suggested that there had been a ferocious eruption of methane gas, and the ship was found right in the center of the crater, sitting upright.

Unfortunately, no one has ever made a direct observation of a methane gas eruption. This means no one knows how big of a bubble it could make or if a methane gas bubble could sink a ship. To test their prediction that the methane gas bubbles could sink a ship without warning, May and Monaghan returned to the lab and began conducting experiments.

The scientists created a model that allowed them to test what would happen to a boat if a large bubble came up from underneath the surface near a ship. They recorded their experiments with a video camera to study later and show to others. Their lab experiments showed that a large gas bubble could cause a ship to sink if the ship was in just the right spot!

There is still no direct evidence of this occurring in the ocean, but scientists are on their way to explaining how some ships mysteriously sink into the depths of the ocean.


Student Page 5.2A: Gases in the Ocean 16�

Student Page 5.2A: Gases in the Ocean (continued)

Think and Write1. How is the process that May and Monaghan went through to try to explain “What sunk that ship?” similar to the process that you have been using in this unit to explain “What makes things float?”

2. Think about the fluids involved in May and Monaghan’s explanation of what caused the ship to sink—methane gas and ocean water. Which fluid is less dense? Use evidence from the story to support your answer.

3. Think about the forces involved in May and Monaghan’s explanation.

3a. Why would a ship float on water, but sink once a methane gas bubble was underneath it? Explain your answer using the terms buoyant force and gravitational force.

3b. Draw two pictures: One that shows the forces acting on the ship when water is underneath it, and a second that shows the forces acting on the ship when methane gas is underneath it.

4. Imagine that you were given the opportunity to continue May and Monaghan’s investigation into “What sunk that ship?” Explain what your next step would be.

Teacher Page 5.2a: Gases in the Ocean 167

Imagine working for a fishing company. Each day you would load up the boat with fishing gear, maps, and other supplies. You would head out to sea and spend the day catching fish to sell on the mainland. Some days you would catch many fish, the sun would shine, and the ocean would be calm. Other days things might not go so well. What might a really bad day on a fishing boat be like?

Fishing all day and not catching anything? Losing your nets? Being out all day in rain and rough waves? None of those things would make for a nice day at sea, but worst of all might be the boat, without warning, sinking like a stone to the bottom of the ocean. Truly, a fishing company’s worst nightmare!

Luckily for fishing boats it does not happen very often, but there are many tales of boats sinking without warning, especially in particular parts of the ocean. The Witches Ground in the North Sea between Scotland and Norway is one area that has a reputation for sinking ships. Scientists sent a remote controlled submarine down to one of the sunken vessels to help determine what caused it to sink. They found it sitting upright, telling them it was not the result of a hole in the hull or being swamped by large waves. What else might have caused an otherwise seaworthy boat to sink like a stone?

This question intrigued scientists from all around the world. Australian scientists David May and Joseph Monaghan studied the Witches Hole area extensively. They conducted surveys of the ocean floor around the sunken boat looking for anything that seemed unusual. They discovered that the boat was right in the middle of what appeared to be a large crater, and all around it were methane hydrate deposits.

May and Monaghan knew that methane hydrate deposits were evidence that methane gas was

Teacher Page 5.2a: Gases in the Ocean

under the ocean floor. Other scientists had already discovered that methane gas is released from decomposing organic matter deep underneath the ocean. The gas works it way upwards to the ocean floor, and under the enormous pressure of the ocean water it does not escape. Instead, it can form methane hydrate deposits.

Based on their observations and the work of other scientists, May and Monaghan made an important prediction. They predicted that if the methane hydrate deposits were disturbed, the methane gas below them could escape. This would create bubbles at the surface, possibly very large bubbles, which could have sunk the ship. They had two key pieces of evidence for their prediction. The crater suggested that there had been a ferocious eruption of methane gas, and the ship was found right in the center of the crater, sitting upright.

Unfortunately, no one has ever made a direct observation of a methane gas eruption. This means no one knows how big of a bubble it could make or if a methane gas bubble could sink a ship. To test their prediction that the methane gas bubbles could sink a ship without warning, May and Monaghan returned to the lab and began conducting experiments.

The scientists created a model that allowed them to test what would happen to a boat if a large bubble came up from underneath the surface near a ship. They recorded their experiments with a video camera to study later and show to others. Their lab experiments showed that a large gas bubble could cause a ship to sink if the ship was in just the right spot!

There is still no direct evidence of this occurring in the ocean, but scientists are on their way to explaining how some ships mysteriously sink into the depths of the ocean.



Teacher Page 5.2a: Gases in the Ocean (continued)

Think and Write1. How is the process that May and Monaghan went through to try to explain “What sunk that ship?” similar to the process that you have been using in this unit to explain “What makes things float?”

possible answer: There are lots of things that are similar. We both had a question that we were studying. We both looked for evidence and tried to learn from other people investigating the same kind of stuff. We all tested things floating and sinking in the lab. We made predictions, and are trying to explain things we wonder about.

2. Think about the fluids involved in May and Monaghan’s explanation of what caused the ship to sink—methane gas and ocean water. Which fluid is less dense? Use evidence from the story to support your answer.

possible answer: Methane gas must be less dense than water because it rises up above the surface of the water once it gets free from being trapped below the ocean floor.

3. Think about the forces involved in May and Monaghan’s explanation.

3a. Why would a ship float on water, but sink once a methane gas bubble was underneath it? Explain your answer using the terms buoyant force and gravitational force.

possible answer: The ship could float on water because the buoyant force from the water was equal to its weight and held it up. The ship sank once there was methane gas underneath it, because the buoyant force from the gas is much less. The buoyant force must equal the weight of the fluid that a floating object displaces in order for it to float. Gas is a lot less dense than water, so the buoyant force from gas is a lot less than the buoyant force from water. It must have been less than the gravitational force on the boat that was pushing down.

3b. Draw two pictures: One that shows the forces acting on the ship when water is underneath it, and a second that shows the forces acting on the ship when methane gas is underneath it.

possible answers: The gravitational force would be the same in both cases because the weight of the boat does not change. The buoyant force from water is greater than the buoyant force from gas.

water underneath the boat methane gas underneath the boat

The buoyant force is equal to the gravitational force.

The buoyant force is less than the gravitational force.

Gravitational force

Buoyantforce

Gravitational force

Buoyant force


Teacher Page 5.2a: Gases in the Ocean (continued)

4. Imagine that you were given the opportunity to continue May and Monaghan’s investigation into “What sunk that ship?” Explain what your next steps would be.

possible answers: I would watch the videos from May and Monaghan’s lab. I would talk to other scientists that studied methane gas to see if they had an estimate of how big of a gas bubble might happen. I would build more models with different sized boats and different sized bubbles to try to determine how big of a bubble there would need to be to sink different sized ships.

I would also take another submarine to the bottom of the ocean floor to collect samples from the crater and the ship. Then, I would get another scientist to analyze those samples to see if there was anyway to see if the ship sank at the same time as the eruption happened. This would help rule out it being coincidence that the ship was in the middle of the crater.

Step 6 Overview 17�

S T E P

6

Overview: Unit Evaluation

This step provides an opportunity for students to evaluate and apply their understanding of density and buoyancy . In Lesson 1 students work together in small groups to discuss common misconceptions surrounding density and buoyancy in context of the Exxon Valdez oil spill. They develop evidence-based explanations first in groups and then individually.

In Lesson 2 students demonstrate their knowledge and understanding of density and buoyancy and the process of scientific inquiry by designing and conducting a scientific investigation into question of their own about density and buoyancy. To conclude the unit, students are asked to construct an evidence-based explanation for the question they investigated.

Step 6 Lesson 1: Density and Buoyancy Misconceptions: Oil Spill 17�


Key Concepts• Density and a balance of forces

determine whether or not an object will float.

• Common misconceptions can be addressed using evidence-based explanations.


• write evidence-based explanations for scientific questions about density and buoyancy

• use evidence from previous activities, records in science notebook, and logical reasoning to support their claims and assertions when discussing explanations in a group.


MaterialsFor each student• Student Page 6.1A: The Exxon

Valdez• science notebook

Density and Buoyancy Misconceptions: Oil Spill1. Ask students to reflect on the Question Wall and the What Makes Things Float chart to remind students of some misconceptions and key concepts that were investigated throughout the unit.

2. Distribute Student Page 6.1A: The Exxon Valdez and form groups of three. Instruct students to read the essay and then respond to the questions following each statement first as a group and then individually.


REAPS QuestionsR What are some misconceptions that our class

discussed about density and buoyancy when we first started this unit?

E What is an evidence-based explanation? Evidence-based explanations are conclusions drawn from measurements and interpretation of data.

A Explain a quantitative relationship between mass and volume. The ratio of mass to volume is a characteristic property called density.

P Explain what helped you most to understand the factors that determine whether something will sink or float.

S What are you still interested in investigating about density and buoyancy? This question is used to generate student interest for the next lesson where they will conduct their own scientific inquiry into one of the questions from the question wall.

Step 6 Lesson 1: Density and Buoyancy Misconceptions: Oil Spill 177

Implementation Guide1. Prompt students to reflect on the Question Wall and initial ideas recorded in the first lesson of this unit.

• Guide a discussion about the misconceptions that they identified early in the unit

• Use the What Makes Things Float chart to reflect on the key concepts that were studied throughout the unit.

• Explain that some of these misconceptions and key concepts will be in the problems students are about to work with in this lesson.

2. Distribute Student Page 6.1A: Exxon Valdez and divide the class into groups of three. Assign who will be the first recorder for the group and explain that each group member will be a recorder and write the responses to the questions following one of three statements in this lesson.

3. Explain that students will work in groups (of three) to tackle misconceptions that someone might think about an oil spill. As a group, they must decide what to write in response to the questions and statements.

• Students may draw on information from their science notebooks but should record their answers by consensus as a group.

• Students should also respond using evidence to the questions individually. Remind students that their answers may differ from the answers of the group.

The chart on the following page is a sample scoring rubric for the student responses.


Criteria Excellent Missing Some Important Details

Needs Substantial Improvement

Concept:Showing understanding that density and a balance of forces determine whether or not an object will float.

1a. Author explains that displacement of liquid influences how an object heavier than water can float.1b. Author recognizes that lighter refers to weight (or mass) in the statement but it would be more accurate to say density.2. Author identifies correct units of volume and methods for measuring volume of liquids and solids.3. Author correctly identifies relationship between mass and volume in terms of density.

Author refers to most concepts in the response (as outlined in previous column) but is inaccurate or incomplete in some explanations.

Author makes few or no references to the scientific terms and concepts (as outlined in the first column).

Presentation Author uses all scientific terms correctly and appropriately.Author’s ideas are logically organized and easy to read and understand.Grammar, spelling, and structure of the story are all accurate and strong.

Author uses 75% of the scientific terms correctly and appropriately.Author’s ideas make a good story and are usually easy to understand.Most grammar, spelling, and structure is correct.

More than 50% of the time, author uses scientific terms incorrectly or inappropriately.Author’s ideas are difficult to understand. Grammatical, punctuation, or spelling errors are significant and interfere with the story.

Student Page 6.1A: The Exxon Valdez 179

It was just after midnight on March 24, 1989. A large ship carrying over 53 million gallons of crude oil was moving through the water near the southern Alaskan coast. Suddenly the ship ran aground, hitting a reef that punctured its hull. About 11 million gallons of oil leaked out into the sea. This incident is known as the Exxon Valdez oil spill and was one of the largest oil spills in U.S. history.

Student Page 6.1A: The Exxon Valdez

Think and WriteBelow are some statements that someone may think about the Exxon Valdez incident. After the statements, are questions. As a group, discuss and respond to the questions.

• After each statement, assign a recorder to write your group’s answer or question. Assign a new recorder after each statement, so that each group member takes a turn recording a group response.

• Discuss the questions as a group and refer to your science notebooks for help.

• The recorder only writes a response that the entire group agrees to.

• After the group responds, individually, record your own response to the questions. Your response can be different from the group response.

• Be sure to use evidence and explain your reasoning in both your group and individual responses.

Statement A

Before the tanker hit the reef, it surely floated on the water as it was carrying its cargo of oil. But the large ship was made mostly of steel! Steel is much heavier than water. Things float because they are lighter than water. It is surprising that such a heavy boat could float at all.

Discuss these questions as a group. Then, have the recorder write down your group’s responses to the questions. After the group creates an explanation, write down your own individual explanation. Be sure to use evidence in all explanations.

A-1 How could such a heavy boat float?

A-2 Explain how you would change the following statement to make it scientifically accurate: Things float because they are lighter than water.

A-3 What does “lighter” really mean in the statement: Things float because they are lighter.

When the oil leaked out of the tanker, it was carried as far as 500 miles away from the wreck. The oil killed countless birds, fish, and other wildlife in a beautiful part of Alaska. Although it was not the largest spill ever (in terms of amount of oil spilled), it was widely publicized because of the environmental impact. Many people remember the incident vividly to this day.

Student Page 6.1A: The Exxon Valdez 181

Statement B

When the Valdez ran aground, it leaked 11 million gallons of oil. That much oil could fill about 125 Olympic-sized swimming pools. Those are about the size of a large community, high school, or university pool, and that ship held 125 of them! That seems like a lot of oil for a boat to be able to carry.


B-1 What determines how much oil a boat can carry?

B-2 What is the scientific term for how much space an object occupies?

B-3 How can this amount be measured for a liquid and for a solid?

Student Page 6.1A: The Exxon Valdez (continued)

Statement C

The oil that leaked out the ship was thick and dark. The oil looks much heavier than water. If that was true, it seems like the oil that leaked out of the Valdez should have sunk to the bottom of the ocean. But, the pictures show that it was floating on the surface of the water. I don’t understand how something so thick, dark, and heavy looking could be floating on top of water.


C-1 Why does oil float on top of water?

Step 6 Lesson 2: Inquiry into Density and Buoyancy 18�


Key Concepts• Scientific investigations are

usually directed by a specific testable question and involve collecting relevant evidence and using logical reasoning to develop evidence-based explanations.


• design and conduct a scientific investigation into a question that interests them, and logically create and communicate the explanation to their question.


MaterialsFor each student• science notebook• 1 copy of Student Page 6.2A:

Scientific Investigation

For each investigation group of 1–4 students• materials required for their

investigation (primarily the materials used throughout the unit)

For the class• list or poster of the questions

students developed throughout this unit for the Question Wall

Inquiry into Density and BuoyancyNote: Students have already investigated, practiced, and explained the concepts supported in this unit. In this optional lesson, students explore still unanswered questions from their Question Wall in a student-centered investigation.

1. Remind students that throughout this unit, they have not only been learning about what makes things float, but they have also been acting like scientists. Prompt them to share what they have been doing that is like the work that scientists do.

2. Explain that in this lesson students will have another opportunity to engage as a scientist in studying what makes things float. Direct attention to the Question Wall, pointing out that there are still many unanswered questions. Provide students with Student Page 6.2A: Scientific Investigation and ask individual students to record a question from the wall that they are interested in investigating. Encourage them to revise the wording and specifics of the question as needed to make it testable and/or more specific. Possible testable questions:

• If you mixed sugar water in one vial and salt water in another vial, would they float differently in water?

• Which other block could we add to sinking wood block to make it just barely float?

• How many paper clips would it take to get that diet soda to sink?

3. Allow students to work individually or in groups with other students interested in the same or similar questions. Depending on the way this investigation is structured, students could conduct these investigations independently over the span of a week or more, and present the results to the class on a scheduled date.

4. Provide materials time for students to design an experiment to gather evidence for explaining an answer to their chosen question.

• Travel group to group to offer guidance as needed. Students should construct their explanations using terms like density, buoyant force, gravitational force, weight, and volume.


REAPS QuestionsR What types of qualitative and quantitative observations

did you make in your investigation? Qualitative observations may include noticing if something is submerged or partially submerged or noting that the uneven sides of the boat disrupted the experiment. Quantitative observations may include measuring volumes or weights of objects or tallying the number of pennies a boat can hold.

E What did you learn about density or buoyancy in your investigation? Students’ responses to this question will vary, but need to be supported with evidence directly from their investigation.

A Choose another activity from earlier in this unit and explain how it is related to your investigation? Students’ responses will vary, but should highlight specific investigations and clearly connect them directly to their own investigation.

P If you were asked to conduct another scientific investigation, what is an important thing you hope to remember about conducting it? Use these responses to determine the types of support students will need during future scientific investigations.

S How is making a prediction before beginning a scientific investigation useful to you? Students may suggest that making a prediction helps them remember what they were thinking before they began the test or that predicting first helps them get their thoughts organized before trying to collect data and then explain something new.

Student Page 6.2A: Scientific Investigation 18�

Planning an Experiment to Answer a Question

Question we hope to answer with evidence from this experiment:

First Step: What key decisions were made to plan the experiment?

What do you think the explanation for what will happen is? Why do you think that?

Second Step: What careful steps were taken to set up the experiment?

What are the next key steps that will take place?

What results are we looking for?

Student Page 6.2A: Scientific Investigation

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