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1 Genre Comprehension Skill Text Features Science Content Nonfiction Main Idea and Supporting Details Captions Labels Energy Glossary Scott Foresman Science 3.13 ì<(sk$m)=bdiefg< +^-Ä-U-Ä-U ISBN

2 Vocabulary absorb electric charges electric circuits electric current kinetic energy potential energy reflect refract thermal energy by Margo Tong Picture Credits Every effort has been made to secure permission and provide appropriate credit for photographic material. The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions. Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd). 6 Getty Images; 8 Getty Images; 9 Kindra Clineff/Index Stock Imagery; 10 VCL/Spencer Rowell/Getty Images; 14 Getty Images; 16 David Wrobel/Visuals Unlimited; 21 Digital Vision. Scott Foresman/Dorling Kindersley would also like to thank: 1, 13 Marconi Instruments Limited/DK Images; 19, 22 (R) Stephen Oliver/DK Images. Unless otherwise acknowledged, all photographs are the copyright of Dorling Kindersley, a division of Pearson. ISBN: Copyright Pearson Education, Inc. All Rights Reserved. Printed in the United States of America. This publication is protected by Copyright, and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic, mechanical, photocopying, recording, or likewise. For information regarding permission(s), write to Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois V

3 Energy Suppose you and your family are going to spend a day at the beach. All of you get up early, put on your swimsuits, and eat breakfast. You pack some towels, beach chairs, an umbrella, and beach toys. Everyone puts on hats and sunglasses. You put all the things you need into the car, and you re off! Your parents park the car at a beach parking lot. You walk to the beach, where you find the perfect place on the warm sand. There you spread out the towels, set up the chairs, and open the umbrella. You take out your toys and start digging in the sand. You are ready to have fun. You use a lot of energy to get to the beach. Energy is the ability to do work or cause change. Nothing happens without energy. Much of what we know about the universe comes from the study of energy. There are many forms of energy and many ways to transmit energy. There are many ways to change energy, and many ways to store energy. The Sun is the main source of energy for Earth. Keep reading to find out how its energy powers and shapes life on Earth! The Sun is Earth s main source of energy. 2 3

4 The Sun s energy has different forms. One form is heat. Heat energy is created by reactions inside the Sun. Heat travels to the Sun s surface and then to Earth. It causes ice to melt and water to evaporate. The uneven heating of Earth s land and air causes wind, rain, and other forms of weather. Light is another form of energy from the Sun. Like heat energy, it is created inside the Sun and then travels to Earth. Light energy helps plants grow. There would be no life on Earth without heat energy and light energy. There are other kinds of energy. You probably used some energy this morning. Did you turn on a light when you got up? If you did, the light used electrical energy. The food you ate for breakfast has chemical energy. If you listened to the radio, you used sound energy. Your family used the mechanical energy of the car to get to the beach. Many of the energies listed are combined with other energies. For example, a light wastes some energy. That wasted energy is heat energy. To turn on the radio and use its sound energy, you need to use electrical energy. And the chemical energy created by the gas in a car gives it the mechanical energy needed to drive. Eating breakfast gives us energy. 4 5

5 What is stored energy? Do you like to swim when you are at the beach? If you do, you will need to use energy stored in your body. Stored energy is potential energy. It is inside both people and things, waiting to be released. Whenever an object is at rest, it has potential energy. The object uses its potential energy when it starts moving. An example of an object with potential energy is a rollercoaster sitting at the top of a hill. The rollercoaster uses its potential energy as soon as it starts moving downhill. Potential energy changes to a form of energy to do work or to cause change. For example, the stored energy in your body is chemical energy. It comes from the energy in food. Airplanes also use chemical energy. It is released when jet fuel is burned. Work has to be done to change potential energy. In the case of the rollercoaster, gravity works to make it roll downhill. In the case of the food you eat, your body works on it to change it to chemical energy. 6 7

6 What is energy of motion? Are you ready for that swim? The minute you start to swim you have kinetic energy, the energy of motion. Everything that moves has kinetic energy. Buses, spinning tops, running animals, and other moving things all have kinetic energy. Friction goes against kinetic energy, changing it to heat. Without a new source of kinetic energy, all objects in motion eventually come to a stop. Playing and swimming are forms of kinetic energy. Fast-moving water has a lot of kinetic energy. Many years ago, people figured out a way to use that energy. They built dams to speed up the flow of river water. The water was used to power waterwheels. The waterwheels were part of factories built along riverbanks. The kinetic energy of the water turned the wheels. The wheels were attached to factory equipment inside. The equipment worked because it used kinetic energy created by the moving water. More recently, people figured out how to make electricity from moving water. They built dams that create electricity. These dams change water s kinetic energy to electrical energy. 8 9

7 Changing Forms of Energy Energy can change from one form to another. This morning you ate some cereal. The chemical energy from the cereal was stored as potential energy in your body. That potential energy was changed to kinetic energy when you took a swim. You can get more potential energy by eating lunch. Whenever energy changes form, some of the energy is given off as heat. Your body got warmer when it changed the cereal s chemical energy to kinetic energy. During your swim, some of that kinetic energy heated the surrounding water. Your day at the beach is over. You have gone home. You have had dinner and are ready to watch television. You take the stored chemical energy from dinner and turn it into kinetic energy when you press the remote control. The remote control uses several forms of energy. Its batteries use chemical energy to create an electric current. The current is electrical energy. It creates a beam of light that travels from the remote to the television. The beam is light energy. It turns on the television. The television releases sound and light energy. There is just a little bit of heat coming from the television, too. Eating lunch gives you potential energy

8 How does energy travel? You know that moving objects contain energy. But did you know that some energy travels as waves? Sometimes these waves are easy to see, such as ocean waves or ripples of water. The bigger the wave or ripple, the more energy it carries. Some other forms of energy, such as sound, also move as waves. You cannot see these waves without special equipment. trough crest Sound waves You can measure how much energy is in a wave. The bottom of a wave is called a trough. The top of a wave is called the crest, or peak. Wide waves have lots of space between the trough and crest. They also have lots of energy. The length of an energy wave can be measured too. Find the space between two crests. The shorter the space, the more energy that wave has. Short waves have more energy than long waves. That s why a shortwave radio can pick up sounds from very far away

9 Heat Energy Feel the top of a computer after it has been on for a while. It will feel very warm. The computer s electrical Chocolate energy is giving off heat. If you put a sheet of paper on top of the computer, it will pick up some of the heat. Thermal energy moves as heat from a warmer object to a cooler object. The paper will not get warmer than the computer. It will only get as warm as the computer. Ice cubes Thermal energy can change matter. If you take away enough heat from a liquid, you can freeze it. If you add enough heat to a solid, you can melt it. The very tiny particles that make up all three forms of matter are also moving. They are moving because they have energy. This energy is called thermal energy. Every time these tiny particles move, they give off some heat. Melted chocolate 14 15

10 Lantern fish Light Energy Light is energy that we can see. The Sun produces light every day. Electricity is another source of light. Light can also be made during chemical changes. When fuel is burned, both heat and light are created. A fire in a fireplace keeps you warm. It also gives off a nice glow. Chemical changes in some living things also make light. Some ocean fish make their own light because of chemicals in their bodies. It is very dark deep in the ocean. The light some ocean fish make helps them see. The lantern fish got its name because it makes light in its body. The light attracts both prey and mates. What path does light take? Light takes the shortest and simplest path from one point to another. Light does not turn around corners. An object that blocks light will cast a shadow behind it. Not all objects block out light. Light can pass through glass and clear water. Scientists use different terms to describe light. Making shadows 16 17

11 How does light change? Even though light cannot avoid hitting an object, it keeps moving after it does. Objects reflect or redirect light. Objects with flat, smooth surfaces reflect light very well. Light that bounces off an object keeps moving, but in a different direction. A mirror does this. You can see your own reflection in a mirror because a lot of light reflects off your face. If the light is right, you might see yourself reflected in a lake too. Objects that refract, or bend light, usually make things appear differently from the way they normally do. Things can look bigger or smaller than they really are. They can look longer, shorter, thinner, or wider too. Light refracts because it moves at different speeds through different materials. For example, light moves more quickly through air than it does through water

12 Did you know that sunlight is made of different colors? Red, orange, yellow, green, blue, indigo, and violet are all found in sunlight. Sometimes refraction causes the light to separate into these colors. That s when you can see a rainbow. When light hits an object, it will reflect at least one of these colors. Suppose a book has a blue cover in the sunlight. This means the book is reflecting blue light. The book does not reflect colors other than blue. It absorbs them, or takes them in. A white object reflects all the colors of sunlight. A black object absorbs all the colors. Have you ever noticed that dark objects feel hotter in sunlight? That s because a lot of the absorbed sunlight turns into heat. Polar bears reflect and absorb sunlight. Their fur looks white because it reflects some of the sunlight. However, underneath their fur polar bears have black skin that absorbs the rest of the Sun s light and changes it to heat. This is part of the way that polar bears stay warm during cold arctic winters

13 Electrical Energy The particles that make up matter have both negative and positive electric charges. An electric charge is a tiny amount of energy. An object can be positively charged or negatively charged. Positively charged objects attract negatively charged ones. This means that positively charged particles pull negatively charged ones toward themselves. Objects with the same charge repel one another. This means two negatively charged particles will push each other away. Positive and negative charges are everywhere. Magnets have positive and negative charges. Lightning is caused by positive and negative charges. Even your body contains substances that are positively and negatively charged. An electric current is the flow of electric charges from one place to another. Electric circuits are pathways that control the flow of the current. Circuits are usually made with metal wires. This is because metals are very good at moving electricity from one place to another. When you flip a switch, you are closing a circuit. Once the circuit is closed, the electric current flows. The electricity that runs through your home travels on an alternating current. Alternating currents change direction at certain times. Some industries use direct current, which does not change direction. Electricity powers many of the everyday objects we use. How many can you name? 22 23

14 Glossary absorb electric charges electric circuits electric current kinetic energy potential energy reflect refract thermal energy take in or suck up tiny amounts of energy controlled pathways that electric charges travel on the movement of electrical energy the energy of motion energy stored in objects and living things to bounce off an object and go in a different direction to bend and change direction the total energy of all the particles in matter What did you learn? 1. Why does light refract? 2. Where do you get potential energy? 3. What are two examples of the Sun s energy? 4. In this book you have read about waves and energy. Write to explain how you can tell if a wave has a lot of energy or a little energy. Use the words trough and crest in your answer. 5. Main Idea and Supporting Details Electrical charges can be positive or negative. What details from the book help you understand how charges move? 24