Properties of Matter. Describing Matter Matter exists in one of three states: ◦Solid ◦Liquid...
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Transcript of Properties of Matter. Describing Matter Matter exists in one of three states: ◦Solid ◦Liquid...
Properties of Matter
Describing Matter Matter exists in one of three states:
◦ Solid◦ Liquid◦ Gas
• All matter is made up of elements or compounds which exist in the form of molecules and atoms
• The spacing between molecules in a substance and the way the molecules move determines the state of the substance
What determines the space? The spacing between molecules is determined by cohesive and adhesive forces
A cohesive force is the term used to describe molecules that are strongly attracted to one another
An adhesive force is the term used to describe the attraction between molecules that are different. They explain why paint sticks or adheres to wood and why oil lubricates a machine
Solids Solids have very strong cohesive forces
The molecules in solids are packed closely together allowing for little movement
This is why solids retain their shape
Liquids• Cohesive forces in liquids are not as strong as in solids so the molecules are further apart and can move
around more
• This extra movement allows liquids to take the shape of their container
• Liquids have strong adhesive forces which allow them to adhere to surfaces
• Oils make good lubricants because of the way they adhere to metal surfaces
• The adhesive force in liquids allows them to act as coolants because they reduce friction
Gases The molecules in gases have almost no cohesive force
Individual molecules are spaced far apart, allowing them more freedom of movement
Because there is little cohesive force in gases, they will expand to fit any container
Mechanical Properties Mechanical Properties describe how a material will behave when it is used in different situations such as supporting a weight or resisting friction
These properties describe how materials like concrete, wood, steel, and glass will react when they are used in mechanical situations including carrying weight
Mechanical Properties of Solids The mechanical properties of solids are different than those of liquids or gases
They include: stress, elasticity, strength, hardness, malleability, ductility, cohesion, adhesion, and tensile strength
We would use these properties to describe the solid
Stress Stress is an important consideration when choosing appropriate building materials in construction
Too much stress results in damage to materials and buildings
The physical effect of stress on materials is called strain and describes how solid materials react to external forces
The four types of external forces that cause stress are tension, compression, shear, and torque
Stress Tension – stretches or pulls materials. It effects the supporting wire cables used in a pulley system on a crane. When a crane lifts a weight, the wires are stretched. If the weight is too heavy, the wires will snap. Over time, the cables are weakened and must be replaced
Compression – shrinks or pushes against materials. For example, the concrete foundation of a building is under constant stress from compression caused by the weight of the floors above
Shear – shifts or cuts materials. Bolts or welds that hold two pieces of metal together experience this type of stress. If the bolts or welds are not strong enough to withstand shear, they will snap. Shear can also cause cracks in materials
Torque – twists or turns materials. For example, moving parts such as drive shafts in heavy equipment are subject to this type of stress. The hoist lines on cranes are subject to torque because of shifts in the weight as it is being lifted and effects of wind
Elasticity Elasticity is described as the ability to return to original shape after subjected to a force such as tension, compression, shear, and torque
A skyscraper can sway several feet in a horizontal direction without damaging its structural integrity
Concrete and steel cores in these buildings help make them more rigid to control heavy swaying
Elasticity – Ultimate Strength The elastic limit of a material describes the maximum limit to which a material can be twisted or bent and still recover its original shape
Ultimate strength describes the point at which material finally breaks.
These two physical properties are important safety considerations
For example, if wire for a crane is stretched beyond its elastic limit, it will deform and have a weak spot. This damage is permanent and the wire must be replaced.
Hardness Hardness describes the material’s ability to resist being damaged
It is associated with durability and abrasion resistance
A harder material is more resistant and durable
Steel and glass are both hard materials that are used in construction of buildings
Malleability Malleability describes the material’s ability to be rolled, bent, or pressed into different shapes
Aluminum and copper are good examples of malleable metals and are often used for architectural features
Think about how easy it is to crush an aluminum can
Brittleness Brittleness is the opposite of malleability
Cast iron and glass are brittle
Cast iron will break or crack if it is bent
Malleability is important in the piping and sheet metal trades
For example, plumbers need to be able to bend pipe to fit into different spaces
Ductility Ductility describes the ability of a material to be stretched into wires or rods
Aluminum, gold, silver, and copper are examples of highly ductile materials
Aluminum can be drawn through a hole to produce a small diameter wire used in welding.
Steel is also highly ductile and is used in the form of steel rods to strengthen concrete. The steels rods and be bent and formed into different shapes
Cohesion Cohesion describes the force of attraction between molecules of the same type
Cohesion is what holds molecules together in solid form
Adhesion is the force of attraction between molecules of different kinds
Tensile Strength Tensile strength depends on cohesive force
It is the force needed to break or pull apart the material
For example, steel has a greater tensile strength than copper. This means it takes a greater force to break or pull apart steel than copper
Tensile strength is measured in PSI (pounds per square inch)
Mechanical Properties of Solids We just learned about stress, elasticity, ultimate strength, hardness, malleability, ductility, cohesion, adhesion, and tensile strength – all mechanical properties of solids
Engineers and architects must consider properties of materials like wood, concrete, steel, iron, and glass because they have different strengths and weaknesses
Building materials are often used in combination to strengthen mechanical properties
Examples Concrete has strong compression and shear mechanical properties, but weak tensile strength
Reinforcing concrete with steel rebar increases the tension for concrete and makes it much more resistant to breaking apart and cracking
The steel bars are placed to carry the tensile stresses
Reinforced concrete is used to make columns, wall footings, and slabs in buildings
Examples Suspension bridges suspend the roadway from huge main cables that extend from one edge of the bridge to the other
The cables rest on top of high towers and are secured at each end by anchors
Most of the weight of the bridge is carried by these cables
The cables are made of thousands of small steel wires that are bound together
Steel is strong under tension. As traffic moves over the bridge, the steel changes shape because of stress and then returns to its normal shape
Mechanical Properties of Liquids Liquids include paints, solvents, coolants, and fuels
Liquids behave differently than solids because the molecules are further apart
The mechanical properties of liquids include: Viscosity, Surface Tension, Buoyancy, Volatility, Cohesion, and Adhesion
Viscosity Viscosity describes how thick a liquid is and how it flows
Viscosity can be used to describe all liquids but it is most commonly used to describe engine oils, paint, and machine lubricants
Heavy equipment such as bobcats and backhoes require different oil viscosities at different temperatures
Colder temperatures require thinner, less viscous oil than that required in summer temperatures
Using the wrong oil could result in damage to the engine and other machine parts
Surface Tension Surface tension describes how the surface of a liquid behaves like a skin that allows certain objects to float
Surface tension can be a good or bad thing
For example, surface tension can stop a liquid from thoroughly wetting a surface.
In hydraulics, oils that bead up on a surface instead of spreading evenly mean uneven wear on surfaces because only part of the surface is being lubricated
Solvents Solvents are used in liquids to reduce viscosity and surface tension
This allows for paint to flow more easily
Reduced surface tension allows paint to coat more easily
Buoyancy Buoyancy is the terms used to describe why objects float in liquids
An object will float if the buoyant force is greater than the weight of the object
This happens because all objects lose a part of their weight when they are submerged in water
In water, we can lift a heavier object than we could in air
This is because the buoyant force of the water lifts the part of the object
Volatility Volatility measures how quickly a liquid vaporizes
A liquid is highly volatile if it changes quickly from a liquid to a gas
The vapours from highly volatile materials can be very dangerous because they are explosive or flammable when the are exposed to heat or air
Gasoline, turpentine, alcohol, and paint thinners are highly volatile
Physical Properties Physical Properties describe characteristics that are part of the material based on the combination of elements that make it up
Electrical conductivity, thermal conductivity, thermal expansion, and corrosion resistance all describe physical properties of matter
Electrical Conductivity Electrical Conductivity describes the ability to conduct an electrical current
Gold, silver, copper, and aluminum are examples of materials that are excellent conductors
Copper and aluminum are commonly used to make electrical wire
Materials that are poor conductors are also important because we use them to insulate
Glass and rubber make poor electrical conductors but they are great insulators
Thermal Conductivity Thermal conductivity measures the rate that heat travels through a material
Welders need to know about this physical property of metal because they must be careful not to overheat it
Overheating metal can change how it will behave under stress.
Thermal Expansion Thermal expansion describes the increase in size of a material when it is heated
Solids, liquids, and gases expand when heated or contract when cooled
Thermal expansion is the reason expansion joints are replaces on bridges
The roadway on a bridge can expand up to a meter in length during the summer
Corrosion Resistance Corrosion resistance describes a material’s ability to resist combining with other elements
Materials react to the environment they are used in
For example, oxidization is the term used to describe rust formation
Rust is probably the most common type of corrosion
The effects of oxidization on other metals like aluminum oxides actually helps to protect the aluminum
Measuring Matter In order to use materials effectively and safely, there must be a way to measure them
Matter – whether in the form of solid, liquid, or gas – is measured using volume, density, and pressure
Volume Volume measures how much space an object takes up or occupies
In the metric system, volume is measured in cubic centimetres (cm³), cubic metres (m³) and litres (L)
In the Imperial system, volume is measured in cubic inches (in³), cubic yards (yd³), quarts, and gallons
Density Density measures the ratio of a mass to a volume
Density compares the masses of equal volumes of different kinds of matter
Density cannot be measured directly. It is calculated after the mass and the volume of the material is known
Density We normally measure density using kg/m³ or g/cm³
When talking about density, we normally compare our objects to water, which has a density of 1 g/cm³
If an object has a lower density than water, it will float
If an object has a higher density than water, it will sink
MassMeasurement of the amount of matter
(or stuff) in an object◦ Measured in grams (g)
There are 3 states of matter:
Solid
Liquid
Gas
VolumeMeasurement of the amount of space an object takes up
◦ Measured in milliliters (ml) or cm3
Which do you think would have the greater volume? The greater mass?
Why?
1 kg of feathers 1 kg of rocks
Density is defined as mass per unit volume. It is a measure of how tightly packed and how heavy the molecules are in an object. Density is the amount of matter within a certain volume.
Density
Which one is more dense?Demonstration: People in a square
How about this: Which square is more dense?
Which one is more dense?
Now which one is more dense?
To find the density
3- Divide Density = Mass g Volume c³
1- Find the mass of the object
2- Find the volume of the object
1- Find the mass of the object
ALWAYS REMEMBER
UNITS!
1) Find the mass of the object
2) Find the volume of the object
3) Divide : Density = Mass - Volume
To find density:
Ex. If the mass of an object is 35 grams and it takes up 7 cm3 of space, calculate the density.
1) Find the mass of the object
2) Find the volume of the object
3) Divide : Density = Mass - Volume
To find density:
Ex. If the mass of an object is 35 grams and it takes up 7 cm3 of space, calculate the density
Set up your density problems like this:
Given: Mass = 35 grams Unknown: Density (g/ cm3) Volume = 7 cm3
Formula: D = M / VSolution: D = 35g/7 cm3
D = 5 g/cm3
Let’s try some density problems together Work on these problems with your neighbor
1 Frank has a paper clip. It has a mass of 9g and a volume of 3cm3. What is its density?
2. Frank also has an eraser. It has a mass of 3g, and a volume of 1cm3. What is its density?
3. Jack has a rock. The rock has a mass of 6g and a volume of 3cm3. What is the density of the rock?
4. Jill has a gel pen. The gel pen has a mass of 8g and a volume of 2cm3. What is the density of the rock?
Change Mass AND Keep Volume Same
Increase the mass increase density
Decrease the mass decrease in density
Which container has more density?
A B
Ways to Affect Density
Change Volume AND Keep Mass Same
Increase the volume decrease density
Decrease the volume increase density
Which container has more density?
A B
Ways to Affect Density
In your notebook illustrate the answer to the following question:
What 2 ways will INCREASE density?
What 2 ways will INCREASE density?
Keep the same mass AND decrease the volume
Keep the same volume AND increase the mass
Liquid Layers
If you pour together liquids that don’t mix and have different densities, they will form liquid layers.
The liquid with the highest density will be on the bottom.
The liquid with the lowest density will be on the top.
Objects or substances with MORE density will sink below objects or substances with LESS density
◦ Which do you think is MORE dense,Water or Oil???
Water, Oil…and a SuperballThe oil is less dense than the water, so it’s on top. The superball is less dense than water, but more dense than oil, so it sinks to the bottom of
the oil layer, yet floats on the top of the water layer.
If you have 2 or more substances,
the MORE dense substance will be on bottomThe LESS dense substance will be on top
The density of five liquids are measured as follows:◦ Liquid 1: 1.0 g/mL◦ Liquid 2: 1.38 g/mL◦ Liquid 3: 0.77 g/mL◦ Liquid 4: 2.95 g/mL◦ Liquid 5: 0.056 g/mL
Draw a picture of all 5 liquids in a test tube how they would layer according to density
Liquid 5
Liquid 3
Liquid 1
Liquid 2
Liquid 4
Liquid LayersCheck out this picture. Which layer has the highest density?
Which layer has the lowest density?
Imagine that the liquids have the following densities: ◦ 10g/cm3. 3g/cm3.◦ 6g/cm3. 5g/cm3.
Which number would go with which layer?
10 g/cm3
3 g/cm3
6 g/cm3
5 g/cm3
Liquid Layers – Try with your neighbor
Which liquid has the highest density?
Which liquid has the lowest density?
Which liquid has the middle density?
Liquid Layers Try on your own!
Imagine that the liquids on the right have the following densities:◦ 15g/cm3 10g/cm3
◦ 3g/cm3 9g/cm3
◦ 7g/cm3 12g/cm3
Match the colors to the correct densities.
3g/cm3
7g/cm3
9g/cm3
10g/cm3
12g/cm3
15g/cm3
ReviewWhat is the formula for density?
What happens if you pour together liquids that have different densities?
Will the liquid on the top have the highest or lowest density?
Will the liquid on the bottom have the highest or lowest density?
Super Scientist Question of the Day
Jake has a book, a ruler, and a balance.
How can Jake find the density of the book with the tools he has?