California science grade 5 (8)

Heat moves in a predictable flow from warmer objects to cooler objects until all the objects are at the same temperature... Students know energy can be carried from one place to another

Chapter 3 Chapter 4

The Sun produces more energy in one second than all the people who ever lived have ever used.

Heat Energy

How does heat move from

one object to another?

158

6 PS 3 Heat moves in a predictable flow from warmer

objects to cooler objects until all the objects are at the

same temperature.

159

MAGAZINE ARTICLE

ELA R 6.2.3 Connect and clarify main ideas

by identifying their relationships to other sources and related topics • ELA W 6.2.1 Write narratives.

160

by Fiona McCormack

A group of strange-looking cars recently zipped through Australia The vehicles looked like spaceships, but they were

solar-powered cars

The cars and their drivers were

competing in the World Solar Challenge,

a 1,877-mile solar-car race The cars, with one driver in each, raced from Darwin to Adelaide, Australia Twenty-two teams from 11 countries competed The winning car, from the Netherlands, finished in about 29 hours

Solar cars run on sunlight instead of gasoline Flat solar panels line the outside

of the cars The panels catch sunlight and turn it into electricity to power the cars’ motors With this power, solar cars can travel up to 74 miles per hour

Solar cars aren’t advanced enough to replace gas-powered cars yet But the race demonstrates that their future is bright

Write About It

Response to Literature This article describes how people use energy from the Sun to run solar cars In what other ways do people use the Sun’s energy?

Is the Sun’s energy always useful? Write a personal narrative about how the Sun affects your life What role does the Sun play in your activities?

- Journal Write about it online

@www.macmillanmh.com

from SCHOLASTIC NEWS

161

Lesson 1

Heat Flow

Have you ever been to the desert? During the day

the air and the ground can be very hot At night the

air cools quickly However, if you touch the ground,

you’ll find that it stays warm for a while longer than

the air does How reliable is your sense of touch in

determining how hot or cold an object is?

6 PS 3.a Students know energy can be carried from one place to another by heat fl ow or by waves, including water, light and sound waves, or by moving objects.

162

ENGAGE

What do you think will happen if you place a jar

of warm water into a bowl of ice water? Make

a prediction and test it Then analyze and present

Do you think heat flows between warm objects and

cool objects? What will happen if a jar of cool water

is set into a bowl of room-temperature water? Write

your answer as a prediction in the form “If a jar of

warm water is set into a bowl of room-temperature

water, then If a jar of cool water is set into a bowl

of room-temperature water, then ”

Test Your Prediction

Fill one jar with 30°C water Fill a second jar

with 10°C water.

Measure Place each jar into a separate bowl

of room-temperature water 22°–24°C Record

the starting temperatures of the water in the

bowls and jars.

Experiment Record the temperatures of

the containers every 2 minutes for 20 minutes

Record your observations When do you think

the temperatures will stop changing?

Draw Conclusions

Analyze Make a line graph that shows how

the temperature of the water in each jar and

each bowl changed over time.

Analyze What happened to the temperature

of the jar with warm water? Where did the

heat go?

Step

6 IE 7.c Construct appropriate graphs from data and develop qualitative statements

about the relationship between variables • 6 IE 7.d Communicate the steps and

results from an investigation in written reports and oral presentations.

163 EXPLORE

Molecules in a Solid,

a Liquid, and a Gas

▶ Main Idea 6 PS 3.a

Heat energy flows from a

warmer object to a cooler

object until both are the

Compare and Contrast

How is energy related

to motion?

You know that water can exist as a solid (ice),

a liquid (liquid water), or a gas (water vapor) Did you know that almost all matter can exist as

a solid, a liquid, or a gas? Why? Matter is made

of molecules that are always moving Whether the molecules form a solid, a liquid, or a gas depends on how close together they are and how fast they move Molecules usually move faster in gases and slower in liquids and solids

In solids molecules vibrate back and forth In gases molecules move in straight lines until they bump into other molecules In liquids molecules show a mix of both of these types of motion.The motion of molecules is a type of energy

Energy is the ability to bring about changes or

to do work It takes energy to move yourself up

a hill It takes energy to light a house or cook

a dinner It also takes energy to change ice into water or water into water vapor

/ZWYS

Explore heat fl ow

The molecules in solids, liquids, and gases move at different speeds.

solid

gas

164

EXPLAIN

Two Kinds of Energy

A skateboarder swoops down a hill,

moving faster and faster The energy of

any moving object is called kinetic energy

(ki•NET•ik EN•uhr•jee) A skateboarder has

a lot of kinetic energy as she moves down

a hill The molecules of a gas have a

lot of kinetic energy, too, because

they are moving quickly

When the skateboarder skates up

the hill, she is storing energy The

energy stored in an object by changing

its location is called potential energy

Moving an object upward against

gravity is one way to give it potential

energy At the top of the hill, as the

skateboarder waits to start downhill,

she has the most potential energy

Any moving object, from a molecule

to a car, has energy due to its motion

When you kick a soccer ball, it has

kinetic energy as it sails across

the field

Quick Check

Compare and Contrast How are

kinetic energy and potential

energy similar and different?

Critical Thinking What kind

of energy would a person at

rest have, and why?

▼ As the girl moves downhill, her potential energy is converted into kinetic energy.

165 EXPLAIN

How is temperature

different from heat?

If you place a thermometer in

boiling water, it registers 100°C

(212°F) The thermometer measures

the temperature of the water The

temperature of a substance is the

average kinetic energy of its molecules

Molecules in all substances are

constantly in motion The molecules

in a gas move about rapidly, colliding

with one another They have a great

deal of energy The molecules in a

solid vibrate in place They have less

energy than the molecules in a gas

Some molecules in a substance

may move faster or slower than

other molecules Scientists calculate

the average speed to determine the

molecules’ average kinetic energy The

average kinetic energy of the molecules

determines how much heat a material

has The average kinetic energy

is its temperature

Before a balloon can fly, the air inside

it must be heated The molecules in the air inside the balloon move farther apart Now the air in the balloon is not as dense as the air that surrounds the balloon The balloon floats high into the sky.

166

EXPLAIN

If you hold a mug of hot cocoa,

energy moves to your hand because

the mug has more heat than your

hand Your hand becomes warm If

you drop an ice cube into a hot drink,

energy passes out of the drink into

the colder ice The ice melts, and your

drink cools off

This energy is called heat Heat

flow is the transfer of energy from

a warmer object to a cooler object

When you heat something, such as a

cup of soup, you increase the energy

of its molecules Before it is heated,

the soup has little thermal energy If

you heat soup for a period of time,

it becomes hotter and cooks the

ingredients

Because heat is a form of energy,

it can be measured The most common

unit used to measure heat is the calorie

A calorie is the amount of energy needed to raise the temperature of

1 gram of water by 1°C There is another way to think of heat Heat is energy that flows between two objects that have different temperatures That energy is heat

Heat Flow

Heat flows from warmer objects

to cooler ones Water is heated on the stove Then the hot water is mixed with cocoa The warm mug transfers heat to the girl’s hands.

167 EXPLAIN

Why does heat flow from

one object to another?

Why did the temperatures change over time?

Clue: Compare the temperatures of the water in the bag and in the beaker at the beginning and at the end of the experiment.

Reading Diagrams Measuring Heat Flow

placed into the beaker of warm water

in the illustration below

When someone who has a fish tank brings a new fish home from the store, the fish often comes in a small plastic bag partly filled with water It is important to balance the temperature of the water in the bag with the temperature of the water

in the tank That way the fish is not harmed To balance the temperature, many people place the plastic bag in the tank After an hour or so, the water in the bag will be about the same temperature as the water in the tank Then it will be safe to pour that water, and the fish, into the tank

When you put your hand into

warm water, energy moves to your

hand because the water is warmer

than your hand The opposite is also

true When you put your hand into

cold water, energy passes out of your

hand into the cold water

Energy is transferred from

one object to another because of

differences in temperature Heat

flow is the transfer of energy from a

warmer object to a cooler object Heat

energy always flows from a

higher-temperature material to a

lower-temperature material That is why the

plastic bag became warm when it was

168

EXPLAIN

How Heat Travels

What happens when you dip a

metal spoon into a steaming bowl of

soup? The heat from the hot liquid

causes the molecules in the spoon to

heat up and vibrate faster They collide

with the molecules next to them,

which in turn start vibrating faster,

and so on all the way up the spoon

Eventually the extra energy reaches

the top of the spoon If you touch the

spoon, it will feel hot Heat energy

has flowed from the hot soup to the

top of the spoon to your hand

A thermometer uses heat flow

to measure the temperature of a

material Most thermometers measure

temperature by using a liquid that

expands in warmer materials and

contracts in cooler materials When

Different Objects, Different Temperatures

Observe Touch a metal object, such as a stapler Then touch a wooden object, such as a ruler

or a desk What do you notice?

Predict Do you think that the

metal and the wood are the same temperature? How could you determine whether they are the same temperature?

a thermometer is placed in something warmer or cooler, heat flows between the two until their temperatures are equal The liquid inside the thermometer then registers the same temperature as the material it is in

Quick Check

Compare and Contrast Compare heat flow between a hot object and a cold object with heat flow between two objects at the same temperature

Critical Thinking Describe how

an ice cube cools off a hot drink

▲ This blacksmith uses heat

flow to shape iron.

169 EXPLAIN

What is insulation?

Have you ever wondered why some

objects feel colder than others? For

example, touch the metal leg of a desk

or a chair Then touch the wooden

surface of a desk or a bookcase The

metal feels colder than the wood

Touching a cold object transfers heat

from your body to the object The

effect on the object depends on whether

it is a conductor or an insulator

A conductor is an object that

absorbs heat and distributes it evenly throughout an object Most metals are good conductors They absorb heat and distribute it evenly throughout an object Since the object heats slowly,

it takes time before a change can be observed

An insulator is an object that

absorbs heat but does not distribute

it evenly Wood is an example of an insulator If you place your hand

on a piece of wood, the area under your hand warms up However, the temperature of the rest of the wood does not change

Insulation (in•suh•LAY•shuhn) is used to prevent heat from flowing

into or out of a material You insulate

something by wrapping it with a material that is not a good conductor

of heat Think of a window or the walls in a building On a cold day, the insulation in the wall keeps the heat inside Because heat does not move well through the insulation, the heat does not warm up the entire wall

How can a vacuum bottle keep liquids hot

or cold for a period of time?

Clue: Look at the layers in the vacuum bottle.

Reading Diagrams

Quick Check

Compare and Contrast How do insulators differ from conductors?

Critical Thinking Explain why it

is important to insulate buildings

in hot and cold climates

Writing Link Math Link

Write a Newspaper Article

Write a brief article for a science

newspaper about a new roller coaster

at an amusement park Be sure to

include information about the potential

and kinetic energy of the ride.

Measure Temperature

A pot of water was brought to

a boil at 100°C Then it was cooled for 10 minutes If the water cooled at

a rate of 4°C per minute, what was the final temperature?

to cooler objects

(pp 168–169)

Think, Talk, and Write Main Idea flows from

a warmer object to a cooler object.

Vocabulary When a river flows over

a cliff, its is converted into

.

Compare and Contrast How does heat

differ from temperature?

Critical Thinking If boiling water were

poured into a china cup and a foam cup, which cup would feel hotter? Explain.

Test Practice Which of the following

Test Practice How does energy

transfer from a warmer object to

the titles shown On

the inside of each tab,

compare and contrast

the terms on each tab.

Summarize the Main Idea

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EVALUATE

Scientists experiment by performing

procedures under controlled conditions that

help them test a hypothesis, discover an

unknown effect, or illustrate a known effect

or scientific law.

Sometimes an experiment does not

produce the expected result Does this mean it

was a failure? No It just means that you have

new data to lead to more experiments.

Learn It

When you experiment you perform a test that

supports or does not support a hypothesis You

need to plan a procedure, make observations,

and record data Once you have enough data,

you can draw a conclusion about whether or not

your data supports your hypothesis, it may, or it

may not Either outcome is good However, the

more data you collect, the more accurate your

conclusion will be In the following experiment,

you will collect data to test the following

hypothesis: If a rubber band is thick, then it

will get hotter than a thin rubber band when

both are stretched the same amount.

Try It

▶ You will need a thick rubber band and

a thin rubber band for comparison Without

stretching either rubber band, hold each to your

forehead Do the rubber bands feel warm or

cool? Are they the same temperature as your

skin? Record your observations in a chart similar

to the one shown here.

▶ Hold the thin rubber band away from your face,

and quickly stretch it and let it relax three times

Let it relax, and touch it to your forehead Record

your observation about its temperature in the

chart Repeat this procedure with the thick

172

EXTEND

▶ In an experiment variables are the things that change To

determine what caused the experiment’s results, you need to

change one variable at a time The variable that changes is the

independent variable A dependent variable is one that changes

because of the independent variable In this experiment what is

the independent variable? What is the dependent variable?

Apply It

▶ Now analyze the results of your experiment Do they support

or refute the hypothesis: If a rubberband is thick, then it will

get hotter than a thin rubber band when both are stretched the

same amount? From your results, can you draw a conclusion

about why the stretched rubber band felt warmer than, cooler

than, or the same temperature as your skin? If you used a

thicker rubber band, would the heat flow felt by your skin be

greater, less, or the same?

▶ Can you predict what would happen if you used a thinner

rubber band? A thicker one? A longer one? If you stretched

it five times before feeling it? Ten times? Plan and carry out

an experiment that would prove or disprove one of your

predictions Share the results with your classmates.

173 EXTEND

Lesson 2

At a speed of about 1,230 km (760 miles) per hour,

a plane breaks the “sound barrier.” The plane flies faster

than sound travels Often a cloud of water vapor forms

behind the plane On the ground, you hear a boom that

sounds a lot like thunder Did you know that the boom

you hear is made of waves?

6 PS 3.a Students know energy can be carried from one place to another by heat

fl ow or by waves, including water, light and sound waves, or by moving objects.

174

ENGAGE

How can you change the sound

a string makes?

Form a Hypothesis

What do you think will happen when you stretch a

string out across a desk and use pencils to lift the

string off the desktop? Can you change the pitch of

the sound by moving the pencils? Write your answer

as a hypothesis in the form “If the pencils are moved

closer together, then the pitch of the sound will ”

Test Your Hypothesis

Cut a length of string about twice as long as

your desk Place the string across the desk, and

tie each end to the handle of a bucket so that

the buckets hang freely Insert the pencils under

the string at each edge of the desk Fill each

bucket one-quarter full with stones.

Near the center of the desk, pluck the string

with your finger Record what you hear.

Move the pencils closer together, and repeat

step 2 Record your observations.

Draw Conclusions

Analyze How would you explain what you

observed? Did your observations support

your hypothesis?

Infer How does the tightness (tension)

of a string affect the sound?

What will happen to the sound if you fill each bucket

half full with stones and repeat step 2? Develop

a hypothesis and test it Then analyze and present

your results.

• 2 small buckets

• stones to fi ll each bucket

• 2 pencils

• string or fi shing line

6 IE 7.a Develop a hypothesis • 6 IE 7.d Communicate the steps and

results from an investigation in written reports and oral presentations.

175 EXPLORE

▶ Main Idea 6 PS 3.a

Energy moves from one

place to another by heat

Waves and Energy

One way that energy moves is through wave motion Drop a pebble in a pond, and at first only the moving stone has energy as it falls Then little waves pass over the pond’s surface—another example of energy A few moments later,

a leaf at the edge of the pond bobs up and down

as the wave reaches the shore The waves have carried some of the energy from the dropped pebble across the pond to the leaf

A wave is a disturbance that carries energy from one place to another without a net movement

of matter That means that as a wave travels through water, the water moves up and down, but it doesn’t move in the direction of the wave.The wavelength of a wave is the distance from the top of one crest to the top of the next or from the bottom of one trough to the bottom of the next A wave’s amplitude is the distance from the midpoint to the crest (or trough) of the wave

Wavelength and Amplitude

Ac[[O`g

Explore waves with

a physicist.

▼ A wave can be described

in terms of its wavelength and its amplitude.

176

EXPLAIN

Waves can be measured in different

ways Water waves move up and down

Sound waves move back and forth

The back-and-forth or up-and-down

motion of a wave, sometimes called a

vibration, is described by its frequency

The frequency of a wave tells the

number of vibrations it makes in a

given period of time, usually 1 second

For example, if 2 vibrations occur in

1 second, the frequency is 2 vibrations

Movement of Sound Waves

What would you hear if the boy played the trumpet in a space with no air?

Clue: How does the sound wave travel?

Reading Photos

What is sound?

Toss a pebble into a pond, and the

ripples spread energy outward from

where the stone entered the water Strike

a drum, and the air around it ripples

outward in waves, too Like other forms

of energy, sound travels as waves

A sound wave is produced by the

vibration of an object A sound wave

carries vibration from the vibrating

object outward in all directions For

example, a drum produces sound when

the drum head is struck

A guitar produces sound when a string is plucked or strummed In a saxophone or clarinet, the sound is produced by a vibrating reed The sound of your voice is caused by the vibration of your vocal chords

The pitch, or highness or lowness

of a sound, depends on its frequency

A high-pitched sound, such as that from a flute or a whistle, has a high frequency The vibrations that

produce high sounds move back and forth quickly

178

EXPLAIN

Ear When the trumpet is

played, the air around it

vibrates Your outer ear

directs the vibrations

down the ear canal

Eardrum Inside your

head, the vibrations hit

a membrane called an eardrum and cause it to move back and forth

Ossicles When

the eardrum vibrates, it rattles three tiny bones called ossicles

Cochlea Deep inside the ear, the

ossicles vibrate against the cochlea The vibrations make waves in the liquid inside the cochlea These waves move tiny hairs These hairs send signals along the nerves to the brain As a result, you hear vibrations as sound.

Ear Canal

A low-pitched sound, such as that

from a foghorn or tuba, has a low

frequency The vibrations that produce

low sounds move back and forth at a

slower speed than those that produce

high-frequency sounds

Hearing Sounds

How do we hear sounds? Sound

waves from one vibrating object can

cause other objects, such as your

eardrums, to vibrate You may actually

feel a very loud sound such as a gong

vibrate inside your body or against

the soles of your feet However, most sounds are detected only by our ears The human ear is so sensitive that it can pick up the tiny vibrations in the air that we hear as sounds

Quick Check

Summarize What is the difference between high frequency and low frequency?

Critical Thinking Explain how vibrations from a drum reach your ear

179 EXPLAIN

Clap your hands once Sound waves

spread out in all directions from the

clap A sound wave moves through the

air in the same way that a wave moves

through a coiled spring This kind of

wave is called a compression wave

In sound waves the wave and the

molecules of matter in the wave move

back and forth in the same direction

as the wave

Compression waves move by

compressing and expanding matter

To visualize how a sound wave travels,

picture a coiled spring toy on a table

with someone holding each end If

one person pushes an end of the toy

toward the other person, a wave

travels through the coils from one

end to the other As the wave passes

through each part of the toy, the

wave compresses, or pushes, the coils

together As the wave moves on, the

coils expand, or pull apart

Sound waves are compression waves that travel through the air like the ripples of a coiled spring toy.

Because compression waves need matter to compress and expand,

a sound wave must travel through matter The matter conducts the sound wave away from the vibrating object that produces it

Compression Wave

180

EXPLAIN

Materials That Transmit

Sound Waves

Most sounds that we hear are

transmitted through the air Do you

think that other substances can also

transmit sound? To test this try an

experiment Place a wind-up watch

at one end of a table Then walk to

the other end of the table You cannot

hear the watch ticking Now put

your ear to the table You can hear

the watch ticking because the table

conducts sound waves better than

air does

Sound can travel through solids

and liquids as well as gases In fact,

air is a poor conductor of sound

Sound travels about four times faster

in water than in air and about fifteen

times faster in steel than in air

or a gas?

Traveling Sound Waves

Make a model Stretch a piece

of plastic wrap over a large bowl

or pot Make sure the plastic

is stretched tightly over the container.

Place 20–30 grains of uncooked rice on top of the plastic wrap.

Hold a tin cookie sheet close to the plastic wrap Hit the sheet with

a spoon to make a loud noise What happens to the rice?

Infer What do you think caused the results you observed?

Predict What might happen if you

hit an object that makes a sound different from a cookie sheet?

◀ Sound travels through air, but it does not travel very far from the source of the sound or very fast.

◀ Whales communicate with one another over vast distances The sounds they make can

be detected many miles away Sound travels about four times faster

in water than in air.

181 EXPLAIN

What are electromagnetic

waves?

On a sunny day, you can feel the heat

energy and see the light energy from

the Sun The Sun’s energy is carried to

Earth by electromagnetic waves that

are made up of alternating electric and

magnetic fields These waves are created

by vibrating electric charges

Unlike a sound wave, an

electromagnetic wave vibrates back

and forth across the direction in which

the wave travels Some electromagnetic

waves can travel through matter

However, electromagnetic waves do

not need matter to carry them They

can travel without matter in the almost

complete vacuum of space

We see some electromagnetic waves

as light Light waves are the visible part of the electromagnetic spectrum The electromagnetic spectrum includes

a wide range of electromagnetic energy The lower-frequency waves are radio waves and microwaves Next come infrared waves, which we feel

as heat The higher-frequency waves include visible light and X rays

The prism separates visible light into the colors of the spectrum.

X rays were used to show the bones in this human hand.

Film that is sensitive to

infrared light can show this

night scene at a water hole.

Electromagnetic Spectrum

182

EXPLAIN

Write a Report

Research the history of the invention

of the telephone How did the

understanding of sound waves make

this invention possible? Write a report

and present it to your class.

Make a Graph

Research the wavelengths of different colors of light and the invisible parts of the electromagnetic spectrum Make a color- coded bar graph comparing the wavelengths.

Think, Talk, and Write Main Idea How does energy

move from one place to another?

Vocabulary Amplitude and

frequency are properties that describe a

Summarize How do humans perceive

the difference between sound waves and some electromagnetic waves?

Critical Thinking What kind

of energy is carried by an electromagnetic wave?

Test Practice Which of these

transmits sound least efficiently?

A steel

B a pond

C air

D an ocean

Test Practice The visible part of the

electromagnetic spectrum contains

the titles shown On

the inside of each tab,

summarize how that topic

can help you understand

(pp 178–179)

Electromagnetic waves such as light

also carry energy.

(p 182)

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EVALUATE