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Heat EnergyA Science A–Z Physical Series
Word Count: 947
www.sciencea-z.com
Written by Felicia Brown
Heat Energy
Key elements Used in this BooKthe Big idea: One of the most important types of energy on Earth is heat energy. A great deal of heat energy comes from the Sun’s light hitting Earth. Other sources include geothermal energy, friction, and even living things. Heat energy is the driving force behind everything we do. This energy gives us the ability to run, dance, sing, and play. We also use heat energy to warm our homes, cook our food, power our vehicles, and create electricity.Key words: cold, conduction, conductor, convection, energy, evaporate, fire, friction, fuel, gas, geyser, heat energy, hot, insulation, insulator, lightning, liquid, matter, particles, radiant energy, solid, Sun, temperature, thermometer, transfer, volcano
Key comprehension skills: Cause and effectOther suitable comprehension skills: Compare and contrast; classify information; main idea and details; identify facts; elements of a genre; interpret graphs, charts, and diagrams
Key reading strategy: Connect to prior knowledgeOther suitable reading strategies: Ask and answer questions; summarize; visualize; using a table of contents and headings; using a glossary and bold terms
Heat Energy
Written by Felicia Brown
www.sciencea-z.com
Heat Energy © Learning A–Z Written by Felicia Brown
All rights reserved.
www.sciencea-z.com
Photo Credits: Front cover: © iStockphoto.com/Julien Grondin; back cover, page 5: © iStockphoto.com/ Arpad Benedek; title page, page 20 (left): © iStockphoto.com/Anna Ziska; pages 3, 9, 20 (right): © Jupiterimages Corporation; page 4: © iStockphoto.com/Nancy Louie; page 6 (left): © iStockphoto.com/Sreedhar Yedlapati; page 6 (right): © iStockphoto.com/Diane Diederich; page 7 (left): © iStockphoto.com/Yuri Hnilazub; page 7 (right): © iStockphoto.com/Alexander Hafemann; pages 10, 11: © iStockphoto.com/bubaone; page 13: © iStockphoto.com/Milorad Zaric; page 16 (top): © iStockphoto.com/Mik111; page 16 (bottom right): © iStockphoto.com/Craig Veltri; page 16 (bottom left): © iStockphoto.com/Amanda Rohde; page 21 (top): Sheryl Shetler/© Learning A–Z; page 21 (bottom): © iCLipART.com; page 22: courtesy of NASA/JpL-Caltech
illustration Credits: pages 8, 12, 14, 15, 17, 18, 19: Cende Hill/© Learning A–Z
3 4
Heat energy cooks these marshmallows.Table of Contents
Introduction ...................................... 4
Sources of Heat Energy ................... 5
Temperature .................................... 10
Heat Moves Through Things........ 13
Conduction ...................................... 14
Convection ...................................... 17
Heat Energy and You ..................... 20
Glossary ........................................... 23
Index ................................................ 24
Introduction
Have you ever stood next to a
campfire? Have you ever watched
soup boil? Then you have seen
and felt heat energy at work!
There are many kinds of energy. But
you use heat energy all the time.
In this book, you will learn where
heat energy comes from, how it
moves, and much more.
Sources of Heat Energy
Rub your hands together very fast.
Do they feel hot? The heat is caused
by friction. Friction happens when
two objects rub together. Friction is
one way to make heat!
5 6
Rubbing your hands and wearing warm clothing help keep you warm.
Burning fuel is another way we
get heat. Gasoline is a kind of fuel.
When gasoline burns, it makes heat
energy. The heat energy is used to
make cars and trucks run.
Electricity also makes heat energy.
Toasters, irons, and hair dryers use
electricity to make heat. Electric
furnaces heat homes and schools.
Fuel makes cars run. It also makes the electricity we use every day.
Heat comes from nature, too.
Lightning is a natural source
of heat. And did you know that
Earth has its own heat deep
underground? It is so hot in the
middle of Earth that rocks melt.
Sometimes the melted rocks come
close to the surface and heat water
that shoots out of the ground. This
shooting water is called a geyser.
7
A lot of our energy comes from the
Sun. Have you ever stepped from
the shade into sunlight and felt
warm? Sunlight is radiant energy.
Radiant energy comes in many
different forms. When sunlight
hits your skin, it changes to heat.
Another form of radiant energy
cooks the food in your microwave.8
Nature can melt rocks, heat water underground, and make gorgeous displays of heat energy.
Some of the heat energy radiates away and is absorbed by the atmosphere.Earth receives
light energy from the Sun.
Land, air, and water absorb light energy and warm up.
9
Heat energy always moves from
warm places to cool places. When
sunlight hits the ground, it turns
to heat. Then the heat moves to
the cool air. Heated air keeps
Earth warm.
10
The heat energy of each particle affects how fast it moves.
Temperature
Everything you can touch—all
matter—is made up of particles,
too small to see. These particles are
always moving a tiny bit. Every
object also has heat energy. How
much heat energy an object
has affects how quickly
its particles move. Dark things take in more of the Sun’s energy than light-colored things. That’s why light-colored clothes keep you cooler on a hot summer day. So which would feel warmer: a white rock or a black rock?
We use temperature to know how much
heat energy things have. The hotter
something is, the more heat energy it
has. The more heat energy it has, the
higher its temperature. The higher its
temperature, the faster its particles
move. The less heat energy something
has, the colder its temperature. The
colder its temperature, the more
slowly its particles move.
We use a thermometer
to measure temperature.
11 12
Temperature is measured in degrees
(°) using either the Celsius (C) or
Fahrenheit (F) scale.
Water freezes at 0°C (32°F), and it boils at 100°C (212°F). A thermometer can tell you how hot or cold the water is.
Thermometer comes from two words. Thermo means “heat.” Meter means “an object used to measure.” So a thermometer is an object used to measure how hot something is.When particles have more heat, they
move faster.
Gas: Particles are farthest apart. Heat
moves slowest through a gas.
Heat Moves Through Things
You know that the temperature of
an object can change. Pizza can
be hot from the oven. Later, the
pizza gets cold. The pizza changes
temperature because heat energy
moves through it. Heat energy
moves through solids (such as pizza)
and liquids and gases (such as water
and air). Heat energy always moves
from a warmer object to a cooler
object. But it moves differently
through solids than it moves
through liquids and gases.
13 14
Conduction
Heat moves easiest through solids.
This is because the particles in solids
are closer together than the particles
in air or liquids. Heat moves through
solids by conduction.
Heat moves through particles in pizza.
Solid: Particles are closest together, and in a pattern. Heat moves through easily.
Liquid: Particles are closer together. Heat moves more quickly through a liquid than a gas.
15 16
A good conductor is something that heat can move through easily. Metal is a good conductor. Pots and pans are made of metal
because it helps food cook fast.
A good insulator is something that heat cannot move through easily. Wood and plastic are good insulators. Heat energy moves slowly in these solids. Pan handles are made of wood and plastic because they stay cool.
What happens to the particles in this
metal rod when they touch fire?
First, they get heat energy from the
fire. The heat energy makes them
move fast. The hotter particles bump
into other, cooler particles in the rod.
This makes the cooler particles heat
up and move faster. The heat energy
transfers up the rod until all its
particles are hot. In time, the rod will
be too hot to hold!Travel mugs keep heat in, but oven mitts keep heat out.
A metal pot is a good conductor.
Particles higher up are still cool and slow.
Particles in the fire get hot and move fast.
17 18
Convection
Let’s look at how heat moves
through a liquid, such as soup. A
hot pot heats the soup at the bottom
first. The heat makes these soup
particles move fast. They spread
out. When the particles spread out,
the soup gets lighter! The soup at
the bottom of the pot becomes
lighter than the soup at the top.
Now the soup at the top of the pot
is cooler. It is also heavier, so it
sinks! The heavier, cooler soup
pushes the lighter, hotter soup up to
the top. This is why soup churns
and boils as it gets hot!cool soup
particles close together and moving slowly
particles far apart and moving fast
soup heats up
burner heats the pan
19 20
Heat Energy and You
Your body has ways to keep cool
and stay warm. When you get
too hot, you sweat. As sweat
evaporates from your skin, it takes
heat away from your body. Now
your skin has a lower temperature,
and your body feels cooler. To stay
warm, you wear thick clothes.
They help keep in the heat.Now let’s learn how heat warms gas,
such as air. When the ground warms
the air above it, the air rises. The
heavier, cooler air from above sinks
and pushes the warmer air up.
Cooler air is always sinking and
pushing up warmer air. The moving
air is called wind! Heat energy
moving through liquid or gas is
called convection.Your body needs to stay at about the same temperature, whether it’s hot or cold outside.
Energy from the Sun turns to heat when it is absorbed by the ground. Then heat from the ground warms the air above it. Cooler air from above pushes the warm air up.
21 22
We put insulation in our homes to
help keep out hot air during the
summer. Insulation also helps keep
in warm air during the winter.
You have learned many things
about heat. Heat is one kind of
energy. Heat is an energy that we
use every day. Heat moves through
solids, liquids, and gases. Heat
moves from hot things to cool
things. We use temperature to
tell how hot or cold something is.
Heat energy comes from many
places, such as fuels, the Sun,
and volcanoes.
Imagine being lost outside in the woods. You have no matches to start a fire,
and it is cold. How would you stay warm?
Most of our energy comes from the Sun.
Possible answers: Build a shelter from branches and brush, rub sticks together so friction makes them burn, or pile leaves and grass on yourself to stay warm.
Insulation has many tiny air pockets. Air is a good insulator.
23 24
Glossary conduction the transfer of heat from
one object to another (p. 14)
conductor a material, usually a metal, that transfers heat, electricity, or sound from one object to another (p. 16)
convection the transfer of heat by movement in a liquid or gas (p. 19)
evaporate to change from a liquid state to a gas state (p. 20)
friction a force that builds up and creates heat when two objects rub against each other (p. 5)
fuel any material used to produce heat or power (p. 6)
geyser a hot spring that boils from time to time, sending a column of water and steam into the air (p. 7)
heat energy a form of energy that transfers from an object with a higher temperature to an object with a lower temperature (p. 4)
insulator a material that reduces or prevents the transfer of heat (p. 16)
matter anything that takes up space and has weight (p. 10)
radiant energy energy that travels in waves (p. 8)
temperature the measure of hot and cold, usually measured on a thermometer (p. 11)
thermometer a tool used for measuring temperature (p. 11)
transfer to move from one place to another (p. 15)
Index
cooking, 4, 8, 16–18
particles, 10–11, 13–15, 17, 18
sunlight, 8, 9, 19
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