Heat Energy A Science A–Z Physical Series Word Count: 1,324 Heat Energy Written by Felicia Brown Visit www.sciencea-z.com www.sciencea-z.com 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 Heat Energy 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 Heat Energy © Learning A–Z www.sciencea-z.com Written by Felicia Brown All rights reserved. www.sciencea-z.com Heat energy cooks these marshmallows. Introduction Table of Contents Have you ever stood next to a campfire? Introduction ..............................................4 Have you ever watched soup boil or ice Sources of Heat Energy ...........................5 melt? If so, you have felt or seen heat energy at work! Temperature ............................................10 There are many kinds of energy, such as Heat Moves Through Things................13 sound energy and electrical energy. But Conduction ..............................................14 it is heat energy that we see and feel the Convection ..............................................17 most. We use it to cook our food, heat our houses, and run our cars. Heat Energy and You .............................20 Glossary ...................................................23 In this book, you will learn where heat energy comes from, how it is used, how Index ........................................................24 it moves, and more. 3 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 Fuel makes cars run and makes the electricity we use objects often make more friction than every day. smooth objects, and more friction makes more heat! Burning fuel is another way we make heat. When fuels such as coal, gasoline, and wood burn, they make heat energy. Heat from burning gasoline is used to make cars and trucks run. Electricity is another way we get heat energy. Electric furnaces heat homes and schools. Toasters, irons, and hair dryers are just a few other things that Rubbing your hands and wearing warm clothing help keep you warm. use electricity to make heat. 5 6 Heat energy comes from natural sources, too. Lightning is a natural source of heat Some of the heat that makes air spread out very fast, energy radiates away causing thunder. And did you know and is absorbed by Earth receives the atmosphere. that Earth has its own heat buried deep light energy underground, called geothermal heat? It’s from the Sun. so hot under Earth’s crust that rocks melt. Sometimes the molten rock comes out at Land, air, and water the surface through a volcano. In other absorb light energy places, the molten rock comes close to the and warm up. surface but doesn’t come out. This melted, underground rock can heat water trapped The Sun is our most important source in the ground. The water later shoots out of energy. Have you ever stepped from of the ground as a geyser. the shade into 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 travels to Earth in waves of tiny particles. When sunlight hits your skin, it changes to heat. Your microwave oven uses another kind of radiant energy to Nature can melt rocks, heat water underground, and make gorgeous displays of heat energy. cook your food. 7 8 Heat energy always moves from warmer Temperature places to cooler places. When sunlight All matter—everything that has weight hits the ground, it turns to heat. Then the and takes up space—is made of particles heat moves from the hot ground to the too tiny to see. These particles are cooler air above it. This blanket of air always moving a little bit. Every object around Earth keeps the planet warm. also has heat energy, and the amount of heat energy an object has affects how quickly its particles move. An object Dark things take in more of the Sun’s energy than light-colored things. That’s with less heat energy has particles that why light-colored clothes keep you cooler move more slowly. An on a hot summer day. So which would feel object with more heat warmer in the sun: a energy has particles that white rock or a black rock? move more quickly. The heat energy of each particle affects how fast it moves. 9 10 We use temperature to know 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. Temperature is measured in degrees (°) according to 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 Because boiling water has so much heat thermometer is an object used to energy, the tiny particles in the water measure how hot something is. move very fast. The temperature of boiling water is 100°C (212°F). Ice, or frozen water, has so little heat energy that the tiny particles in it move very slowly. The temperature of frozen When particles have more heat, they move faster. water is 0°C (32°F). 11 12 Heat Moves Through Things Conduction You know that the temperature of an Heat moves most easily through solids. object can change. The water that was This is because the particles in solids are boiling at 100°C (212°F) freezes solid closer together than the particles in air if you leave it in the freezer long enough. or liquids. Heat can quickly transfer And if you leave an ice cube out on a from one particle to another when they plate, it will melt. Other objects change are close together. Heat moves through temperature, too. Pizza that’s hot from the solids by conduction. oven will get cold over time. The water Gas: Particles are farthest apart. Heat moves and pizza change temperature because slowest through a gas. heat energy moves through them. Heat energy moves through solids Liquid: Particles (such as pizza) as well as liquids and are closer together than in a gases (such as water and air). But it gas. Heat moves more quickly moves differently through solids than through a liquid. it moves through liquids and gases. Solid: Particles are closest together and in a pattern. Heat moves easily through particles. Heat moves through particles in pizza. A hot piece of pizza cools down over time. 13 14 Particles higher up are still cool and slow. A good conductor is a material that heat can move through easily. Metal is a good Particles in the fire conductor. Pots get hot and move fast. and pans are A metal pot is a good conductor. made of metal because it helps food cook fast. Other solids, such as wood and plastic, are not good conductors. Heat energy What happens to the particles in this moves slowly in these solids. Solids that metal rod when they touch fire? First, do not conduct heat they get heat energy from the fire. The well are called heat energy makes them move fast. The insulators. Pan hotter particles bump into other, cooler handles are particles in the rod. This makes the made of wood cooler particles heat up and move faster. and plastic The heat energy moves up the rod until because they all its particles are hot. In time, the rod stay cool. Insulated cups keep heat in, will be too hot to hold! while oven mitts keep heat out.