California science grade 5 (8)

Chapter 3

Chapter 4

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


CHAPTER 3

Heat Energy

How does heat move from
one object to another?

158


Lesson

1

Heat Flow

PAGE

162

Lesson

2

Waves

PAGE

174

Lesson

3

Fuels: Our Major
Energy Source
PAGE

186

Lesson

4

Heat Transfer in
Solids and Fluids
PAGE

198

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


Literature
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


from SCHOLASTIC NEWS

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

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?

162
ENGAGE

6 PS 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.


How can you measure heat flow?

Materials

Make a Prediction
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 . . .”

• 2 large bowls
• 2 jars

Test Your Prediction

• 4 thermometers

Fill one jar with 30°C water. Fill a second jar
with 10°C water.

• watch or
stopwatch

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.

• water
Step

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.
Step

Analyze What happened to the temperature
of the jar with warm water? Where did the
heat go?

Explore More
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
your results.
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


▶ Main Idea

6 PS 3.a

Heat energy flows from a

warmer object to a cooler
object until both are the
same temperature.

▶ Vocabulary
energy, p. 164
kinetic energy, p. 165
potential energy, p. 165
temperature, p. 166
heat, p. 167
heat flow, p. 168
insulation, p. 170

-Glossary
@

www.macmillanmh.com

▶ Reading Skill
Compare and Contrast
2WTTS`S\b

/ZWYS

2WTTS`S\b

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.
Molecules in a Solid,
a Liquid, and a Gas

Explore heat flow
with a chef.

liquid

solid
gas

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

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.

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

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?

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.

166
EXPLAIN

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.


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.

Heat
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.

Quick Check
Compare and Contrast How is

temperature different from heat?
Critical Thinking What happens

when you place a hot object in
contact with a cooler one?
167
EXPLAIN


Why does heat flow from
one object to another?
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 highertemperature material to a lowertemperature material. That is why the
plastic bag became warm when it was

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.

Measuring Heat Flow

Reading Diagrams
Why did the temperatures change over time?

168
EXPLAIN

Clue: Compare the temperatures of the water in the bag and in

the beaker at the beginning and at the end of the experiment.


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?

▲ This blacksmith uses heat
flow to shape iron.

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

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.
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.

Vacuum Bottle

vacuum
bottle
mirrorlike
coating
bounces
radiant
heat

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.

vacuum
no material
to conduct
heat between
bottle

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.

inner bottle
outer bottle

Reading Diagrams
How can a vacuum bottle keep liquids hot
or cold for a period of time?

170
EXPLAIN

Clue: Look at the layers in the vacuum bottle.


Summarize the Main Idea
Energy is related to
motion. The energy
of a moving object is
called kinetic energy.
(pp. 164–165)

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
Temperature is the
average kinetic energy
of the molecules in
a substance.
(pp. 166–167)
Heat flow is the
transfer of energy
from warmer objects
to cooler objects.
(pp. 168–169)

Make a
Study Guide
Make a three-tab book
(see pp. 487–490). Use
the titles shown. On
the inside of each tab,
compare and contrast
the terms on each tab.

Writing Link

differ from temperature?
2WTTS`S\b

/ZWYS

2WTTS`S\b

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
is
A
B
C
D

a poor insulator?
wood
copper
rubber
plastic

Test Practice How does energy
transfer from a warmer object to
a cooler object?
A kinetic energy
B potential energy

C heat loss
D heat flow

Math Link

Write a Newspaper Article

Measure Temperature

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.

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?

-Review Summaries and quizzes online @ www.macmillanmh.com

171
EVALUATE


Experiment
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

p
warm u
o
t
e
k
i
l
I
lace.
p
e
r
i
f
e
by th

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.

Kirb y lik
es t o
on the r warm up
a diat or
.

▶ 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
rubber band.

172
EXTEND

6 IE 7.b. Select and use appropriate tools and technology (including
calculators, computers, balances, spring scales, microscopes, and
binoculars) to perform tests, collect data, and display data.


▶ 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

Waves

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?

174
ENGAGE

6 PS 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.

Materials

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 . . .”

• 2 small buckets

Test Your Hypothesis

• stones to fill each
bucket

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.

• 2 pencils

• string or fishing
line
• safety scissors
• safety goggles
Step

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?

Explore More

Step

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.

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


What is a wave?
▶ Main Idea

6 PS 3.a

Energy moves from one
place to another by heat
flow or by waves.

▶ Vocabulary
wave, p. 176
wavelength, p. 176
amplitude, p. 176
frequency, p. 177
sound wave, p. 178
compression wave, p. 180
electromagnetic wave, p. 182
light wave, p. 182

-Glossary
@

www.macmillanmh.com

▶ Reading Skill
Summarize

Ac[[O`g

▶ Technology

Kinetic energy always moves. Wind blows,
water flows, light travels, and electricity passes
through wires. How does energy move from one
place to another?

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.

Explore waves with
a physicist.

Wavelength and Amplitude

176
EXPLAIN

▼ A wave can be described
in terms of its wavelength
and its amplitude.


Wave Frequency

Reading Diagrams
Why does the pelican stay in the same
place?

Measuring Waves
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
per second.

Clue: Look at the way the wave moves.
Watch waves
@ www.macmillanmh.com

Quick Check
Summarize What is the difference

between wavelength and
amplitude?
Critical Thinking How is frequency

related to energy?

177
EXPLAIN


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.

Movement of Sound Waves

Reading Photos
What would you hear if the boy played
the trumpet in a space with no air?
Clue: How does the sound wave travel?

178
EXPLAIN


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.

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

Hearing Sounds

Summarize What is the difference

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

between high frequency and low
frequency?
Critical Thinking Explain how

vibrations from a drum reach

your ear.

Eardrum Inside your
head, the vibrations hit
a membrane called an
eardrum and cause it to
move back and forth.

Ear Canal

Ear When the trumpet is
played, the air around it
vibrates. Your outer ear
directs the vibrations
down the ear canal.

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.

179
EXPLAIN


How do sound waves
travel?
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.

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

A_cSShSQ]WZab]USbVS`
O\R`SZSOaS

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

eOdS[]bW]\

180
EXPLAIN


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

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.

◀ 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.

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.

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?

Quick Check
Summarize Why is water a

better sound transmitter than air?
Critical Thinking Why does the

transmission of sound require
matter such as a solid, a liquid,
or a gas?

181
EXPLAIN