FOCUS ON EARTH SCIENCE (6)

There are different forms 124 Chapter 3 Science Content Standards 3.a Students know energy can be carried from one place to another by heat flow or by waves, including water, light

Thermal Energy and Heat

120

This raging forest fire glows red as it burns the trees and other vegetation in its path The changes caused by a forest fire are due to the release of thermal energy The thermal energy released by the fire causes the high temperatures that help keep the fire going.

-Vˆi˜ViÊÊ+PVSOBM

-Vˆi˜ViÊÊ+PVSOBM List three changes that occur when you light a match.

Feeling The Burn

Thermal energy moves

from warmer to cooler

materials until the

materials have the same

>ˆ˜Ê`i> Energy can

be transferred from one

3.c, 3.d, 7.a 3.a

Tom J Ulrich/Visuals Unlimited

Start-Up Activities

121

How cold is it?

Hot and cold are words

you often use How

accurate is your sense

of hot and cold?

Procedure

1 Complete a lab safety form

2 Fill a pan with lukewarm water Fill a

second pan with cold water and ice Fill

a third pan with warm tap water

3 Put one hand into the cold water and the

other hand into the warm water Keep

your hands in the water for 15 s

4 Quickly remove both hands from the pans

and put them both into the pan of

luke-warm water

Think about This

• Identify which hand felt warmer when

you placed both hands in the lukewarm

water

• Explain whether your sense of warm and

cold would make a useful thermometer

▶ view

▶ explore Virtual Labs

▶ access content-related Web links

▶ take the Standards Check

STEP 1 Fold a sheet of paper into thirds

lengthwise

STEP 2 Unfold and draw vertical lines

along the folds Draw three horizontal lines

to divide the paper into four rows Label as shown

£ Ó

Energy and Change

Make the following Foldable

to record the types of energy and examples of changes caused by the energy

Inferring

As you read this chapter, list in the first column the types of energy discussed In the second column, list an example from the text of a change caused by that energy

In the third column, describe a different change that you know is caused by that type of energy

3.a

ca6.msscience.com

ELA6: R 2.4

Learn It! What should you do if you find

a word you don’t know or understand? Here are some

suggested strategies:

Practice It! Look at the word bonds in

the following passage See how context clues can help you

understand its meaning.

When you eat, you take in another type of tial energy Chemical potential energy is the energy stored in bonds between the atoms that make up matter Remember that atoms are joined together by chemical bonds to form molecules, as shown in

poten-Figure 6 Chemical potential energy can be released

during chemical reactions when these bonds are broken and new bonds are formed.

1 Use context clues (from the sentence or the paragraph) to help you defi ne it.

2 Look for prefi xes, suffi xes, or root words that you already know.

3 Write it down and ask for help with the meaning.

4 Guess at its meaning.

5 Look it up in the glossary or a dictionary.

122

New Vocabulary

Apply It! Make a vocabulary bookmark with a strip of paper As you read, keep track of words you do not know or want

to learn more about.

ELA6: R 1.3

Read a p aragraph

ing a vo cabular

contain-y word f rom beginni ng to en

d Then, g o back to d etermin

e the meanin g of the

word.

1 Energy is the ability to cause change

2 There is only one type of energy

3 Thermal energy always flows from larger objects to smaller objects

4 Only waves can transfer energy from place to place

5 Thermal energy from the Sun travels to Earth as waves

6 Energy can be stored in a stretched rubber band

7 Objects must be touching each other in order for energy to flow from one to another

8 A baseball player can transfer energy to a baseball by hitting the ball with a bat

9 Most materials get smaller when they are heated

10 The atoms and molecules in an object move slower

as the object cools

Before You Read

Target Your Reading

Use this to focus on the main ideas as you read the chapter.

1 Before you read the chapter, respond to the statements

below on your worksheet or on a numbered sheet of paper

• Write an A if you agree with the statement.

• Write a D if you disagree with the statement.

2 After you read the chapter, look back to this page to see if

you’ve changed your mind about any of the statements

• If any of your answers changed, explain why

• Change any false statements into true statements

• Use your revised statements as a study guide

Print a worksheet of

this page at

ca6.msscience.com

Why It’s Important

Energy is the cause of all the

changes you observe in the

world around you.

gravity: attractive force

between two objects that

depends on the masses of

the objects and the distance

between them (Grade 5)

>ˆ˜Ê`i> Energy exists in many forms

Real-World Reading Connection A pizza fresh from the oven sure smells good! When you put it in the oven, it was just soft dough covered with cold tomato sauce, cheese, and uncooked vegetables Now, the dough is crisp and golden, the sauce is hot, and the vegetables are toasted What caused these changes?

What is energy?

Think about the changes you see and feel every day You might have seen cars moving and felt the wind All the

changes around you are caused by energy Energy (EN ur

jee) is the ability to cause change There are different forms

124 Chapter 3

Science Content

Standards

3.a Students know energy can be carried

from one place to another by heat flow or by

waves, including water, light and sound

waves, or by moving objects.

Lesson 1 • Forms of Energy 125

Visualizing Kinetic Energy

Figure 2▲

The amount of kinetic energy of a moving object

depends on the mass and speed of the object Energy is

measured in units called joules (J) For example, the

fastest measured speed a baseball has been thrown is

about 45 m/s The kinetic energy of a baseball traveling

at that speed is about 150 J.

▲ A sprinter with a mass of about 55 kg running at 9 m/s has kinetic energy about

15 times greater than the baseball.

▼ A 600-kg race car traveling at about 50 m/s has about 5,000 times the kinetic energy of the baseball

▲ There is evidence that a meteorite 10 km in

diameter collided with Earth about 65 million

years ago and might have caused the

extinc-tion of dinosaurs The meteorite might have

been moving 400 times faster than the

base-ball and would have a tremendous amount of

kinetic energy due to its enormous mass and

high speed—about a trillion trillion joules.

▼ Earth’s atmosphere is continually

bombarded by particles called cosmic rays, which are mainly high-speed pro- tons The mass of a proton is about a

100 trillion trillion trillion times smaller than the mass of the baseball Yet some of these particles travel so fast, they have nearly the same kinetic energy as the baseball.

Contributed by National Geographic

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Figure 3 The kinetic energy of each vehicle depends on its mass and speed The

truck has more kinetic energy than the blue car because it has more mass The

blue car has more kinetic energy than the green car because it is moving faster.

Compare the kinetic energy of the two cars if they have the same speed.

Kinetic Energy and Speed

In a game of pool, the cue ball hits the rack of balls and causes these balls to move The kinetic energy of the moving cue ball changes the positions and the motions of these other

balls when it hits the rack A greater change occurs when the

cue ball is moving faster Then the balls in the rack move faster and become more spread out This means that the cue ball has more kinetic energy when it is moving faster The faster an object moves, the more kinetic energy it has

Kinetic Energy and Mass

The kinetic energy a moving object has increases as the mass of the object increases Suppose you roll a volleyball down a bowling alley instead of a bowling ball If the two balls have the same speed, the volleyball will knock down fewer pins than the bowling ball Even though the balls have the same speed, the volleyball has less kinetic energy because

it has less mass

Figure 3 shows how the kinetic energy of moving objects depends on their mass and speed The two cars have the same mass, but they don’t have the same kinetic energy The blue car has more kinetic energy because it is moving faster The truck and the blue car have the same speed However, the truck has more kinetic energy because its mass is greater

Units of Energy

Energy is measured in units of joules, abbreviated as J If you dropped a softball from a height of about 0.5 m, it would have about 1 J of kinetic energy before it hit the floor All forms of energy are measured in units of joules

The rock has potential energy

because it is above the ground.

The potential energy of the rock changed the car.

Figure 4 An object can have potential energy

that causes a change to occur.

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Lesson 1 • Forms of Energy 127

Potential Energy—Stored Energy

An object can have energy even if it is not moving Look

at the hanging rock in Figure 4 Would you say it has energy?

Even though no changes are occurring, the rock still has

energy Remember that energy is the ability to cause change

When the rock falls, it causes a change Because the rock had

the ability to cause change before it fell, it had energy as it

was hanging above the car The hanging rock has stored

energy, called potential (puh TEN chul) energy There are

different forms of potential energy

Gravitational Potential Energy

The rock hanging above the ground has a form of stored

energy called gravitational potential energy This form of

energy is due to the downward pull of Earth’s gravity

Gravitational potential energy depends on an object’s mass

and its height above the ground The hanging rock in

Figure 4 has gravitational potential energy due to its height

above the ground

The higher an object is above the ground or the greater

its mass, the more gravitational potential energy it has For

example, the hanging rock in Figure 4 would cause even more

damage if it fell from a greater height More damage also

would be caused if a rock with more mass fell from the same

height The gravitational potential energy of an object

increases if its mass or height above the ground increases

What are two ways to increase an object’s tional potential energy?

gravita-How deep is the crater?

depth of a few inches

3 Measure the mass of a

1 Relate the depth of

the crater to the mass

of the balls

2 Infer how the

poten-tial energy of the balls before they fell depended on their masses.

Figure 5 A spring has

elastic potential energy

when it is compressed

or stretched.

Identify two ways a

spring can store elastic

potential energy.

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Figure 6 The atoms in molecules are held together by chemical bonds that store chemical potential energy.

Elastic Potential Energy

If you stretch a rubber band and then let it go, you know

about another type of stored energy Elastic (ih LAS tik)

potential energy is the energy stored when an object is

squeezed or stretched When you stretch a rubber band, the elastic potential energy of the rubber band increases This stored energy then can cause the rubber band to fly across the room when you let it go

Figure 5 shows the two ways that a spring can store elastic potential energy If the spring is squeezed together, or com-pressed, it has a tendency to change back to its rest length The spring also will return to its rest length if it is stretched Either by compression or stretching, stored elastic potential energy gives an object the ability to change

Chemical Potential Energy

When you eat, you take in another type of potential energy Chemical potential energy is the energy stored in bonds between the atoms that make up matter Remember that atoms are joined together by chemical bonds to form mole-cules, as shown in Figure 6 Chemical potential energy can be released during chemical reactions when these bonds are bro-ken and new bonds are formed You get energy by eating because food contains chemical potential energy Fossil fuels, such as oil and coal, are energy sources because they contain chemical potential energy

S CIENCE U SE V C OMMON U SE

matter

Science Use something that

has mass and occupies space

The weight of an object depends

on the amount of matter it

contains.

Common Use trouble or

diffi-culty What’s the matter with

your CD player?

128 Chapter 3 • Thermal Energy and Heat

Figure 7 Light energy spreads out in all directions from a light source.

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i]Z]diXjeidi]ZXddaZg]VcYh

Figure 8 Thermal energy causes your hands to feel warmer when you hold a cup

of hot cocoa.

Lesson 1 • Forms of Energy 129

Light Energy and Thermal Energy

When you turn on a lamp, a change occurs Light from the

lamp enables you to see objects in the room more clearly

When you turn on a stove to heat a pot of water, a change

occurs Heating the pot causes the temperature of the water

to increase These changes are caused by light energy and

thermal energy

Light Energy

What causes the changes you observe in plants? You may

know that sunlight is needed for plants to grow Sunlight

causes plants to grow because sunlight contains a form of

energy called light energy Light energy is the energy carried

by light waves When you turn on a lamp, the light spreads

out to make a room seem bright Figure 7 shows why light

energy also is sometimes called radiant energy It spreads out,

or radiates, in all directions from its source

Why is light energy sometimes called radiant energy?

Thermal Energy

When you put your hands against a warm cup, as in

Figure 8, you’ve felt another form of energy Thermal

(THUR mul) energy is energy that moves from one place to

another because of differences in temperature Thermal

energy is sometimes called heat energy Like all forms of

energy, thermal energy can cause changes For example, a cup

of hot cocoa is warmer than your hands When you hold a

cup of hot cocoa, thermal energy moves from the hot cocoa

to your hands This causes a change to occur Your hands

become warmer, and the cocoa becomes cooler Thermal

energy always moves from warmer objects to colder objects

LESSON 1 Review

Summarize

Create your own lesson

summary as you organize

an outline

1 Scan the lesson Find and

list the first red main

heading.

2 Review the text after

the heading and list 2–3

details about the heading.

3 Find and list each blue

subheading that follows

the red main heading.

4 List 2–3 details, key terms,

and definitions under

each blue subheading.

5 Review additional red

main headings and their

supporting blue

subhead-ings List 2–3 details about

each.

130 Chapter 3 • Thermal Energy and Heat

The Different Forms of Energy

Energy is the ability to cause change There are different forms of energy, but all forms of energy can cause something

to change A moving object has a form of energy called kinetic energy Kinetic energy increases if the speed or mass

of the object increases

Potential energy is stored energy There are different kinds

of potential energy In this lesson you read about tional potential energy, elastic potential energy, and chemical potential energy

gravita-Finally, thermal energy is energy that moves from place to place because of differences in temperature You will read more about thermal energy in Lesson 3

1 A car traveling along the

high-way has energy due

to its motion 3.a

2 Define thermal energy in your

Understanding Main Ideas

3 Identify the form of energy

the rock has due to its height

4 Describe the two ways a

spring can store energy 3.a

5 Explain why your hands feel

warm when you hold a cup of

6 Organize Information Copy

and fill in the graphic nizer below with information about the different forms of potential energy 3.a

Applying Science

7 Imagine a bowling ball and a

golf ball that have the same kinetic energy Which one is moving faster? If they move at the same speed, which one has more kinetic energy? 3.a

8 Identify the two forms of

potential energy contained in

an orange hanging from the branch of an orange tree 3.a ELA6: R 2.4

LESSON 2

Figure 9 The bowling ball carries energy from the bowler to the pins.

Identify the form of

energy carried by the bowling ball.

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I]Z`^cZi^XZcZg\nd[i]ZWVaa X]Vc\Zhi]Zedh^i^dcd[i]Ze^ch#

Lesson 2 • Energy Transfer 131

Real-World Reading Connection What sports do you like?

Do you like shooting baskets? Maybe you like running, swimming, or riding a bicycle In all of these activities, energy moves from one place to another

Moving Objects Transfer Energy

A moving object transfers energy from one place to another During a baseball game, a pitcher’s moving arm transfers energy to a baseball and makes it move The mov-ing ball then has kinetic energy When the ball hits the catcher’s mitt, this kinetic energy is transferred to the catcher’s mitt

You can see another example in Figure 9 The bowler is able to knock down the pins by using the bowling ball to transfer energy Some of the kinetic energy of the ball is transferred to the pins when the ball hits the pins The energy that is transferred causes the pins to move

Reading Guide

What You’ll Learn

▼Recognize how moving

objects transfer energy

from one place to another.

▼Describe how waves

transfer energy from one

place to another.

▼Explain ways that energy

can change from one form

to another.

Why It’s Important

All sports involve the

transfer of energy and the

conversion of energy from

one form to another.

force: a push or a pull that

one object exerts on another

object (Grade 2)

Science Content

Standards

3.a Students know energy can be carried

from one place to another by heat flow or by

waves, including water, light and sound

waves, or by moving objects.

3.b Students know that when fuel is

consumed, most of the energy released

becomes heat energy.

Figure 10 The boy only does work when

the object moves in the direction of his force.

132 Chapter 3 • Thermal Energy and Heat

Doing Work Transfers Energy

Studying for a test may seem like hard work, but in science, it isn’t work at all

Scientists define work as the transfer of

energy that occurs when a push or a pull makes an object move Recall that a push

or a pull also is called a force Figure 10

shows that pushing on something doesn’t mean that you are doing work Pushing on

a wall might make you feel tired However, because the wall doesn’t move, no work is being done Work is done only when an object moves in the same direction as the force applied to the object

If you pick up a box, however, you do work You pull on the box and cause the box to move upward Your pull is a force that makes the box move, so you have done work Because you increase the height of the box above the ground, the gravitational potential energy of the box increases As you lift the box, you transfer energy to the box The energy you transfer increases the box’s gravitational potential energy By doing work on the box, you transferred energy to the box

Why is no work done when you push on a wall and it does not move?

Waves Transfer Energy

Have you ever been floating in a wave pool? The waves cause you to move up and down as they move beneath you The waves cause your position and motion to change

because they carry energy A wave is a

dis-turbance in a material that transfers energy without transferring matter In a wave pool, some of the energy carried by a water wave is transferred to you as the wave moves past you The energy transferred by the wave causes you to move upward Like moving objects, waves transfer energy from one place to another

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Figure 11 The bobber is not carried along with the wave It returns to its initial position after the wave passes.

Lesson 2 • Energy Transfer 133

Water Waves

The water wave in Figure 11 transfers energy as it moves

horizontally along the surface of the water However, the wave

does not transfer matter from place to place The water wave

causes the bobber to move up and down as it passes After

the wave passes, the bobber is in the same place The bobber

and the water beneath it have not been carried along with the

wave Instead, only the energy carried by the wave moves

along the surface of the water Like all waves, water waves

transfer energy from one place to another, but they don’t

transfer matter

Sound Waves

You can see water waves as they move along the surface of

a pool Energy also can be transferred by waves you can’t see,

such as sound waves Sound waves are caused by the

back-and-forth movement, or vibration, of an object Figure 12

shows how a vibrating drum causes sound waves

When the drummer in Figure 12 hits the drum, the head

of the drum moves back and forth many times each second

Each time the drum head moves, it hits nearby air particles

and transfers kinetic energy to them These particles, in turn,

hit other air particles and transfer kinetic energy When the

drum head moves outward, it causes the particles in air

nearby to be bunched together When the drum head moves

inward, it causes air particles outside the drum to spread

apart In this way, energy travels from the drum through the

air When this energy strikes your ears, your hear the sound

of the drum

Figure 13 Radiant energy

moves from the Sun to Earth

as electromagnetic waves.

Figure 14 The energy carried by electromagnetic waves is used in different ways.

Identify the type of electromagnetic wave being used in each photo.

134 Chapter 3 • Thermal Energy and Heat

Electromagnetic Waves

Like sound waves and water waves, light is also a type of wave However, unlike water waves and sound waves that can travel only in matter, light waves also can travel in empty space For example, the Sun gives off light waves that travel almost 150 million km to Earth through empty space, as shown in Figure 13 Light waves are a type of wave called elec-tromagnetic waves Electromagnetic waves are waves that can

transfer energy through matter or empty space The energy

carried by electromagnetic waves also is called radiant energy

Types of Electromagnetic Waves

There are other types of electromagnetic waves besides light waves, as Figure 14 shows Radio waves are used to carry the signals you hear when you listen to the radio Microwaves are electromagnetic waves that heat food in a microwave oven Microwaves also are used to carry signals to cell phones The warmth you feel when you sit in sunlight is caused by infrared waves that are emitted by the Sun X rays are used by doctors to diagnose broken bones

ACADEMIC VOCABULARY

transfer (TRANS fur)

(verb) to move something

from one place to another

The doctor will transfer the

patient to a different hospital.

KE PE KE PE KE PE

Figure 15 Kinetic energy is converted into potential energy as the ball

rises Potential energy is converted into kinetic energy as the ball falls.

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X]Zb^XVaediZci^VaZcZg\n#

A^\]iZcZg\n I]ZgbVaZcZg\n A^\]iZcZg\n I]ZgbVaZcZg\n

Lesson 2 • Energy Transfer 135

Energy Conversions

Energy comes in different forms and can

be converted from one form to another

Converting Potential Energy and

Kinetic Energy

When you throw a ball upward, as in

Figure 15, energy changes form As the ball

moves upward, the ball’s kinetic energy

changes into potential energy When the ball

reaches its highest point, all its initial kinetic

energy has been converted to potential

energy Then, as the ball falls down, potential

energy is converted back into kinetic energy

Converting Chemical Potential Energy

As the wood burns in Figure 16, it gives off

light energy and thermal energy Chemical

potential energy is energy stored in the bonds

between the atoms that make up wood As a

result, the molecules in the wood contain

chemical potential energy When the wood

burns, chemical reactions occur that change

chemical potential energy into thermal

energy and light energy

Wood is an example of a fuel, a material

that can be burned to release energy For

example, when wood is burned, most of the

chemical energy changes form Only a small

fraction of the wood’s original chemical

potential energy remains in the ashes, like

those shown in Figure 16

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Figure 17 The kinetic energy of the bicycle is transformed into heat energy due to friction.

Explain why applying the

brakes brings the bicycle to

a stop.

Converting Thermal Energy to Kinetic Energy

Thermal energy from burning fuels can be used to perform work As the gasoline in a car’s engine burns, most of its stored chemical potential energy changes to thermal energy The thermal energy produced by the burning gasoline causes forces to be exerted on parts of the engine These forces make various parts in the car’s engine move These moving parts

do work by making the car’s wheels turn

However, in a car’s engine, only about one-fourth of the thermal energy produced by burning gasoline is converted into kinetic energy The other three-fourths of the energy is transferred to the engine and the surrounding air This causes the engine and other parts of the car to become hot

What happens to most of the chemical potential energy in gasoline when it is burned in an engine?

Converting Kinetic Energy to Thermal Energy

A car’s engine changes some of the chemical potential energy in burning fuel to the kinetic energy of the moving car But as the car moves, some of this kinetic energy is con-verted back into thermal energy The conversion of kinetic energy to thermal energy in a car is due to friction between

the moving parts in the car Friction (FRIK shun) is the force

that resists the sliding of two surfaces in contact

It is friction that causes a bicycle to stop when you apply the brakes, as shown in Figure 16 When you apply a bicycle’s brakes, the brake pads rub against the wheels Friction between the brake pads and the wheels changes the kinetic energy of the wheel to thermal energy As a result, the bicycle stops In a similar way, a car’s brakes use friction to change the kinetic energy of the car to thermal energy

2 Rub lotion on your

hands and repeat

Analysis

1 Describe how the

tem-perature of your hands

changed

2 Identify what energy

transformation

occurred when you

rubbed your hands

together.

3 Infer why moving parts

in engines and other

machines are coated

LESSON 2 Review

Lesson 2 • Energy Transfer 137

What have you learned?

Energy can be transferred in different ways Moving objects

can transfer energy when they collide with other objects

Water waves, sound waves, and electromagnetic waves can

also transfer energy as they move from place to place

You also read about converting energy from one form to

another One example of energy conversion is the burning of

fuels Fuel contains chemical potential energy stored in the

bonds between atoms and molecules When this energy is

released, it can be converted into thermal energy and radiant

Create your own lesson

summary as you write a

newsletter

1 Write this lesson title,

number, and page

num-bers at the top of a sheet

of paper

2 Review the text after

the red main headings

and write one sentence

about each These will be

the headlines of your

newsletter

3 Review the text and write

2–3 sentences about each

blue subheading These

sentences should tell who,

what, when, where, and

why information about

each headline.

4 Illustrate your newsletter

with diagrams of

impor-tant structures and

pro-cesses next to each

2 Gasoline in a car is the car’s

_, because the car’s engine converts the chemical potential energy of the gasoline to thermal energy and

kinetic energy 3.b

Understanding Main Ideas

3 List three types of energy

4 In which of the following

is work NOT done on the

A lifting a box from the floor

and placing it on a table

B holding a box above your

head

C carrying a box up the stairs

D lowering a box from a table

to the floor

5 Describe three ways energy can

be transferred by waves 3.a

6 Give an example not

men-tioned in the lesson of energy changing from one form to

7 Analyze what happens to

most of the energy that is released when firewood is

Applying Science

8 Determine Cause and Effect Copy the graphic orga-

nizer below and list the results

of applying the brakes on a

9 Suggest reasons why

scien-tists might try to design cars that can convert light energy from the sun to kinetic energy

Waves ca6.msscience.com

138 Chapter 3 • Thermal Energy and Heat

Thermal Expansion

Thermal expansion of materials is an increase in the volume of the

substance resulting from an increase in temperature The linear

ther-mal expansion coefficient is change in length of a bar per degree of

temperature change It is measured in parts per million (ppm) per °C

The table below shows linear thermal expansion coefficients for some

common substances To find the volumetric thermal expansion

coef-ficient, multiply the linear thermal expansion coefficient times three.

Practice Problems

1 Find the volumetric thermal expansion coefficient for gold.

2 Find the difference in the volumetric thermal expansion

coef-ficient for aluminum and the volumetric thermal expansion

coefficient of gold.

Linear Thermal Expansion Coefficients

For more math practice,

visit Math Practice at

ca6.msscience.com.

LESSON 3

Figure 18 Matter is made of particles that always are moving with different speeds in random directions.

Lesson 3 • Temperature, Thermal Energy, and Heat 139

Temperature, Thermal Energy, and Heat

pan-What is temperature?

You probably use the word temperature often On a cold

or hot day, you may ask a friend what the temperature is You know that cooking changes the temperature of food

But what does the word temperature really mean?

Particles in Motion

Look around you at objects that are sitting still These objects, and all matter, contain particles such as atoms and molecules that are always moving Figure 18 illustrates that even though the object is not moving, the particles that make it up are constantly in motion

Reading Guide

What You’ll Learn

▼Recognize that thermal

energy flows from a warmer

object to a cooler object.

▼Explain how temperature

depends on particle

motion.

▼Compare different

temperature scales.

Why It’s Important

You use thermal energy

every time you cook food.

speed: a measure of how

quickly an object changes

its position (Grade 2)

Science Content

Standards

3.a Students know energy can be carried

from one place to another by heat flow or by

waves, including water, light and sound

waves, or by moving objects.

7.c Construct appropriate graphs from

data and develop qualitative statements

about the relationships between variables.

Figure 19 Heating the

balloon causes the

parti-cles to move faster and

take up more space.

140 Chapter 3 • Thermal Energy and Heat

Temperature and Particles in Motion

The temperature of an object depends on how fast the ticles in the object are moving The balloon in Figure 19 con-tains particles of air that always are moving Because these particles are moving they have kinetic energy However, these particles don’t move with the same speed Some are moving faster and some are moving more slowly Recall that kinetic energy increases as the object moves faster This means the particles that are moving faster have more kinetic energy Because particles in the balloon are moving at different speeds, they have different amounts of kinetic energy

par-Temperature is a measure of the average kinetic energy of the

particles in a material When the particles in a material move faster, they have more kinetic energy As a result, the average kinetic energy of the particles increases and the temperature

of the material increases

What is temperature?

Thermal Expansion

Something happens to the balloon in Figure 19 as it’s heated by the hair dryer—it gets larger Heating the balloon changes the motion of the particles in the balloon

As the temperature of the air in the balloon increases, the particles in the balloon move faster As the particles move faster, they tend to move farther apart This causes the air in

the balloon to expand Thermal expansion (THUR mul • ihk SPAN shun) is an increase in the volume of a substance when

the temperature increases Most materials expand when their temperature increases Usually, the greater the increase in temperature, the more the material expands

volume (VAWL yewm)

(noun) the amount of space

occupied by an object or a

region of space

A basketball has a larger

volume than a tennis ball.