Heat Energy A Science A Z Physical Series Word Count: 1,301 Heat Energy Written by Felicia Brown Visit www.sciencea-z.com www.sciencea-z.com
Heat Energy Key elements Used in This Book The 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, geothermal heat, geyser, heat energy, hot, insulation, insulator, lightning, liquid, matter, particles, radiate, radiant energy, solid, Sun, temperature, thermometer, transfer, volcano Key comprehension skill: Cause and effect Other suitable comprehension skills: Compare and contrast; classify information; main idea and details; identify facts; elements of a genre; interpret graphs, charts, and diagram Key reading strategy: Connect to prior knowledge Other suitable reading strategies: Ask and answer questions; summarize; visualize, using a table of contents and headings; using a glossary and bold terms Photo Credits: Front cover: istockphoto.com/julien Grondin; back cover, page 5: istockphoto.com/ Arpad Benedek; title page, page 20 (top): istockphoto.com/anna Ziska; pages 3, 9, 20 (bottom): 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/allen Johnson; 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 left): istockphoto.com/amanda Rohde; page 16 (bottom right): istockphoto.com/craig Veltri; 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 Written by Felicia Brown www.sciencea-z.com Heat Energy Learning A Z Written by Felicia Brown All rights reserved. www.sciencea-z.com
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 3 Introduction Have you ever stood next to a campfire? Have you ever watched soup boil or ice melt? If so, you have seen or felt heat energy at work! There are many kinds of energy, such as sound energy and electrical energy. But it is heat energy that you see and feel the most. We use it to cook our food, heat our houses, and run our cars. In this book, you will learn where heat energy comes from, how it is used, how it moves, and more. 4
Sources of Heat Energy Have you ever wondered about all the ways we get heat energy? One easy way to make heat is with friction, or the rubbing together of two objects. Rub your hands together very fast. Can you feel the heat? Rough objects often make more friction than smooth objects, and more friction makes more heat! Fuel makes cars run and makes electricity we use every day. Burning fuel is another way we make heat. When fuels like coal, gasoline,. and wood burn, they make heat energy. Heat from burning gasoline is used to make cars and trucks drive. Rubbing your hands and wearing warm clothing help keep you warm. Electricity is another way we get heat energy. Toasters, irons, and hair dryers are just a few things that use electricity to make heat. Electric furnaces heat homes and schools. 5 6
Heat energy comes from natural sources, too. Lightning is a natural source of heat that makes air spread out very fast (causing thunder). And did you know. that Earth has its own heat buried deep underground, called geothermal heat? It s so hot under Earth s crust that rocks melt. Sometimes the molten rock comes to the surface as a volcano. In other places, the molten rock comes close to the surface,. but doesn t come out. This melted, underground rock can heat water trapped in the ground. The water will come shooting out of the ground as a geyser. Nature can melt rocks, heat water underground, and make gorgeous displays of heat energy. 7 The Sun is our most important source. of energy. Have you ever stepped from the shade into the sunlight and felt warmer? You may think that heat comes straight from the Sun to Earth, but it doesn t. Sunlight is radiant energy. Radiant energy comes in many different forms. When sunlight hits your skin, it changes to heat. Your microwave oven uses another kind of radiant energy to cook your food. 8 Radiant energy from the Sun Earth absorbs Sun s energy Sun s energy turns to heat
Here is a rule about heat energy. Heat energy always moves from warmer to cooler. When sunlight hits the ground, it turns to heat. Then the heat moves from the hot ground to the cooler air above it. This keeps the planet warm. 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 in the sun: a white rock or a black rock? Temperature All matter (everything that has weight and takes up space) is made of tiny particles, too small to see. These particles are always moving, just a little, tiny bit. Every object also has heat energy, and how much heat energy an object has affects how quickly its particles move. An object with less heat energy has particles that move more slowly, and an article with more heat energy has particles that move more quickly. The heat energy of each particle affects how fast it moves. 9 10
We use temperature to tell how much heat energy things have. The less heat energy an object has, the more slowly. its particles move and the colder its temperature. The more heat energy an object has, the faster its particles move and the hotter its temperature. We use a thermometer to measure temperature. 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. Water freezes at 0 Celsius, and it boils at 100 Celsius. A thermometer can tell you how hot or cold the water is. Boiling water has so much heat energy, it makes the tiny particles in water move really fast! The temperature of boiling water is 100 degrees Celsius. When particles have more heat, they move faster. Ice, or frozen water, has so little heat energy that the tiny particles in it move very slowly. The temperature of frozen water is 0 degrees Celsius. 11 12
Heat Moves Through Things You know that the temperature of something can change. The water that was boiling at 100 Celsius freezes solid. if you put it in the freezer long enough. And if you leave an ice cube out on a plate, it will melt. Other objects change temperature, too. Pizza that s hot from the oven will get cold over time. The pizza and water change temperature because heat energy moves through them. Heat energy moves through solids. (like pizza), and liquids and gases (like water and air). But it moves differently through solids than it moves through liquids and gases. Conduction Heat moves most easily through solids. This is because the particles in solids are closer together than the particles in air or liquid. Heat can quickly transfer from one particle to another when they are close together. Heat moves through solids by conduction. Gas: Particles are farthest apart. Heat moves slowest in a gas. Liquid: Particles are farther apart than in solids. It takes longer for heat to move through a liquid. Heat moves through particles in pizza. Solid: Particles are closest together, in a pattern. Heat moves easily through particles. 13 14
Particles higher up are still cool and slow. Particles in the fire get hot and move fast. A metal pot is a good conductor. food cook fast. 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 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 moves up the rod, until all its particles are hot. In time, the rod will be too hot to hold! 15 16 But wood and plastic are solids that. are not good conductors. Heat energy moves slowly in these solids. Solids that do not conduct heat well are called insulators. Pan handles are made of wood and plastic because they stay cool. Insulated cups keep heat in, while oven mitts keep heat out.
cool soup Now the soup at the top of the pot is cooler. It is also heavier, so it sinks! The cool soup pushes the lighter, hotter soup up to the top. Now the heavier, cooler soup takes in heat from the bottom of the hot pot. It will rise to the top of the pot and sink again. This is how soup churns and boils and makes the soup hot! soup heats up fire heats the pan Convection Let s look at how heat moves through. a liquid, like soup. A hot pot heats the soup at the bottom first. The heat makes these soup particles move fast and spread out. When the particles spread out, the soup gets lighter! So the soup at the bottom of the pot is lighter than the soup at the top. 17 18 particles close and slow moving particles far apart and moving fast
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 air up. Now let s learn how heat moves through a gas, like air. When the ground warms air above it, the air rises. The heavier, cooler air from above sinks and pushes the warmer air up. The warm air becomes cool as it moves away from the warmer ground. At the same time, the cooler air that sank toward the ground. is getting heated. Cooler air is always sinking to push up warmer air. This rising and sinking air makes wind! The movement of heat energy through liquids and gases is called convection. 19 20 Heat Energy and You Your body works. to stay at a temperature of 98.6ºF (37ºC). So when you get too hot, you sweat. As sweat evaporates Sweat keeps your body cool. from your skin, it takes heat from your body and releases. it to the air. Now your skin has a lower temperature and your body feels cooler. To stay warm, you wear thick clothes. The clothes you wear when it is cold are a good insulator. They stop the heat from leaving your body. Clothing keeps you warm.
Insulation has lots of tiny air pockets in it. Air is a good insulator. Homes and buildings keep us cool on hot days and warm on cold days. We use fuel to heat our homes. We put insulation in the walls and ceilings of our homes. In the summer, insulation helps keep out the hot air. In the winter, insulation helps keep in the warm air. Imagine being lost outdoors in the woods on a cold day. You do not have matches to start a fire. How would you stay warm? Answers will vary. Possible answers: build a shelter from tree branches and brush, rub sticks together so that friction makes them burn, pile up leaves and grass and crawl under them to stay warm. 21 22 Most of our energy comes from the Sun. You have learned that heat is one of many kinds of energy. It is an important form of energy that we use each day. You have also learned that heat moves through solids, liquids, and gases by passing from particle to particle. You know it moves from hotter areas to cooler areas. Temperature is how we measure how hot or cold something is. There are many sources of heat energy, including fuels, electricity, and natural sources like the sun, lightning, geysers, and volcanoes.
conduction. conductor. convection. evaporate. friction fuel geothermal heat. geyser Glossary.the transfer of heat from one object to another (p. 14).a material that transfers heat from one object to another (p. 16).the transfer of heat by movement in a liquid. or gas (p. 19).to change from a liquid state to a gas state (p. 20).force that builds up when two objects rub against each other (p. 5).any material used to produce heat or power (p. 6).heat energy from inside the Earth in the form of steam or hot water that is sometimes used to produce power (p. 7).a hot spring that boils from time to time, sending a column of water and steam into the air (p. 7) 23 heat energy. insulator. matter radiant energy. temperature. thermometer. transfer. cooking, 4, 8, 16 18.a form of energy that is transferred from an object. with a higher temperature. to an object with a lower temperature (p. 4).material that conducts heat poorly (p. 16).anything that takes up space and has weight (p. 10).energy that travels in waves (p. 8).unit of measure telling how hot or cold something. is (p. 11).a tool used for measuring temperature (p. 11).to move from one place to another (p. 14) Index particles, 10 12, 14 15, 17, 22 sunlight, 8, 9, 22 24