Interface08Intro%20Forces

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IINTRODUCING NTRODUCING FFORCESORCES

9th grade in the Physics First Curriculum

Jaime HortonAmy ScrogginsCarthage R-9 School District

Meera ChandrasekharDorina KosztinDepartment of Physics and AstronomyUniversity of Missouri, Columbia

Support: Missouri Department of Elementary andSecondary EducationMath-Science Partnership Grant

www.physicsfirstmo.org

What is the Physics First program?What is the Physics First program? Physics First is a national movement to teach a

year-long Physics course in 9th grade In Missouri, MO-DESE has funded a partnership

led by Columbia Public Schools and Univ. ofMissouri-Columbia to develop curriculum andconduct professional development (PD)

The first summer of PD was conducted in 2006for 60 teachers, who will return in 2007 and 2008

A smaller protégé class of 22 was accepted for2007 and 2008.

CurriculumCurriculum Year 1: Uniform and Accelerated Motion, Forces,

and Newton’s Laws Year 2: Motion in 2D, Energy, Momentum, and

Electricity Year 3: Electromagnetism, Waves, and Heat Pedagogy - based on Modeling, Inquiry & 5E Year-long follow-up and support

Today - parts of the Unit 3: Introducing Forces

StudentsStudents’’ Beliefs about Beliefs about ForcesForces Only animate objects can exert forces Forces are seen as merely influences on an

object’s motion, not as forces Impetus theory – e.g., force of throw travels with

ball Forces are viewed from the perspective of the

applier, rather than that of the object Tension/Normal forces not well understood

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Learning ObjectivesLearning Objectives A force is an interaction between two objects (an agent

and a receiver) Identify forces acting on an object in terms of a receiver,

one or more agents, effects and direction Draw a force diagram for the object/receiver Describe the parameters that can change/affect amount

of the force State whether resultant force causes the velocity of the

object to be constant or changing Determine if forces acting on an object are

balanced/unbalanced

(GLEs: 2.2.A.a, 2.2.B.c, 2.2.D.c, 2.2.D.d, 2.2.D.e)

Big Understandings and SkillsBig Understandings and Skills Big Understandings:

A force is a push or a pull on an object. A force is a vector - has both amount (magnitude) and direction. A force requires an agent (something does the pushing or

pulling). A force is either a contact force or a long-range force (gravity is

the only long-range force in this unit). The force acting on an object may be the sum of several forces

(net force).

Skills: Identifying forces Figuring out net force

In this unitIn this unit…….. Part 1:

ID different forces, their agents, receivers, effects Investigate in more detail: normal forces, gravity,

friction and elastic forces Part 2:

Forces as vectors Work with several forces acting on an object

draw force diagrams understand graphically how forces balance if forces do not balance, obtain the net force

Activity: Exerting Forces

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Pre-lab questionsPre-lab questions How do you know when you exert a force? Could you make a list of the different forces you

exerted in the last five minutes? How strong a force do you think you can exert? What do you think is meant by the term “force”? What are some things that can happen to an

object when a force acts on it?

Exerting Forces - DirectionsExerting Forces - DirectionsAt each station, create a chart with the following: A picture or diagram showing each situation Are there any forces exerted? What/who is applying the force? What object receives the force? What effect does the force have on the object? What do you think is the name of the force

demonstrated at this station?

Whiteboard feedback from Exerting Forces activity

Two General Categories of ForcesTwo General Categories of Forces

Contact forces – those that require the agentthat causes the force to be in contact with theobject.Examples: pushing, pulling, squeezing,stretching, …..

Field Forces – those that act at a distance.Examples: gravity, magnetism, electricity

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Examples: Contact and Field forcesExamples: Contact and Field forces

Gravity: brings the skier down

Friction: slows you down

Tension: Holds the pot

Normal: holds the owl up

The Four Forces of NatureThe Four Forces of Nature

Many forces on the macroscopic level, such asgravity, friction, elastic, electric, push and pull,centripetal forces

The origins of these forces can be traced to onlyfour fundamental forces: Gravity Electromagnetic Strong Weak

The Four Forces of Nature-2The Four Forces of Nature-2

Gravity – due to the mass of objects. Holdsstars, planets together.

Electromagnetic – due to the charge on objects.Responsible for binding of atoms and molecules.

Strong – holds neutrons and protons together,restricted to the nuclei of atoms

Weak – short-range force, produces instability incertain nuclei

Analyzing ForcesAnalyzing Forces

A force is produced by an agent A force acts on an object – the receiver The force causes something to happen – the

effect

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Analyzing forces Analyzing forces –– Example 1 Example 1

Weight of boy (gravity): Agent – earth; Receiver – boy; Effect – boy slides downward.

Friction: Agent – surface of slide and

boy’s skin and clothes; Receiver – lower surface of

girl’s body; Effect – girl’s downward slide is

slowed down. Weight

Friction

Activity:Identifying and Drawing ForcesPractice III.1 Force Challenge A-D

Forces studied in unitForces studied in unit Four forces are studied in some detail:

Normal force Gravitational force (lab) Friction (lab) Elastic force (lab)

Activity:The Strength of Weight Lab

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Activity:The Strength of Elastic Force Lab

Activity:The Strengthof Elastic Force Lab

Experimental ResultsExperimental ResultsAddedMass(g)

Spring(cm)

RubberBand(cm)

Bungee(cm)

AddedMass(g)

Big spring(cm)

Little Spring(cm)

0 54.1 35.9 55.1 0 15.5 13.9

100 56.4 38.2 55.7 10 19.5 15.9

200 60.5 41.5 56.1 20 23.7 17.9

300 64.4 46.5 56.5 30 27.7 19.8

400 68.6 53.6 57 40 31.8 21.7

500 72.8 57.7 57.5 50 35.9 23.7

600 76.8 61.2 58.8 60 39.8 25.6

700 81.2 63.3 61 70 43.5 27.6

800 85.4 64.5 63.5 80 47.7 29.7

900 89.6 65.3 65.6 90 51.5 31.4

1000 94 65.5 68.3 100 55 33.5

Experimental ResultsExperimental Results

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Stretch (cm)

Mas

s (g)

ConclusionsConclusions Force is directly proportional to stretch Slope of F vs stretch represents the strength of

the spring, k.

[ ][ ]

[ ]

N

m

eFrisek slope

run x

Fk

x

= = =!

= =!

Drawing forcesDrawing forces

Weight

Normal

Weight

Normal

Weight

Normal

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Force Diagrams - Example 1Force Diagrams - Example 1

1. Picture2. Identify System

3. Closed curve

around system

5. Normal

force,FN

6. Force of

gravity, FG

4. Identify contact forces where

system touches the closed curve.

FN

FG

7. ForceDiagram

Force Diagrams - Example 2Force Diagrams - Example 2

Force Diagrams - Example 2Force Diagrams - Example 2 Force Diagrams - Example 2Force Diagrams - Example 2

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FN

FT

FG

7. Force

diagram

Ff


1. Picture

5. (a)Normal

Force FN

6. Force of

gravity FG

5. (b)Tension FT

2-3. Define system and draw

closed curve around it.

4. Contact forces where system

touches curve

FN

FG

FT

7. Force

Diagram

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Next steps...Next steps... This unit then goes on to activities that connect

force to motion The next unit is Newton’s Laws

Contact infoContact [email protected]@Missouri.edu

www.physicsfirstmo.org

If you are a 9th grade teacher and areinterested in this program, please docontact us - we plan to seek funding fora new cycle.

Interface08Intro%20Forces

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