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Heat EnergyA Science A–Z Physical Series

Word Count: 947

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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

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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.

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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.

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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.

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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.

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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

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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.

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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