Genre Comprehension Skill Text Features Science Content Nonfiction Predict Labels Captions Diagrams Glossary Forms of Energy Scott Foresman Science 5.14 ì<(sk$m)=bdjfhg< +^-Ä-U-Ä-U ISBN 0-328-13957-2
Vocabulary conduction convection electromagnetic radiation energy kinetic energy potential energy thermal energy Extended Vocabulary circuit current fossil fuel generator geothermal energy hydroelectric energy nuclear fission renewable resources solar cells turbine by Abbie Farara 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). Opener: Lester Lefkowitz/Corbis; 4 (C) Warren Morgan/Corbis, (B) Bryan F. Peterson/ Corbis; 7 Charles E. Rotkin/Corbis; 8 Charles E. Rotkin/Corbis; 11 (T) Lester Lefkowitz/Corbis; 14 Larry Lee Photography/Corbis;15 (T) Sally A. Morgan/ Ecoscene/Corbis; 16 (B) Francesc Muntada/Corbis; 20 Attar Maher/Corbis; 22 Lester Lefkowitz/Corbis. Unless otherwise acknowledged, all photographs are the copyright of Dorling Kindersley, a division of Pearson. ISBN: 0-328-13957-2 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 60025. 3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05
What You Already Know Scientists define energy as the ability to do work or cause a change. Energy can change from one form to another, but it cannot be created or destroyed. There are many different forms of energy. They include sound, light, electrical, magnetic, chemical, mechanical, nuclear, and thermal energy. Kinetic energy is the energy of motion. The amount of kinetic energy an object has depends on its speed and mass. Heavy, fast-moving objects have lots of kinetic energy. Light, slow-moving objects have less. Kinetic energy can change into other forms of energy. For example, kinetic energy can be changed into electric, sound, or thermal energy. Potential energy, sometimes called stored energy, is energy that is not causing change right now, but could cause change in the future. A skier standing at the top of a steep hill has potential energy. As the skier begins to slide down the hill, potential energy changes to kinetic energy. Potential energy can also be stored in a stretched rubber band or in two magnets that tend to push each other away. A heavy, fast-moving truck has a lot of kinetic energy. Chemical energy is energy that holds atoms together to form molecules. Nuclear energy holds protons together to form the nucleus of an atom. Sound energy is caused by particles vibrating, or moving back and forth, in a pattern called a wave. Light is a form of electromagnetic radiation, which means that it is a combination of both electrical and magnetic energy. Thermal energy is created by the movement of particles inside matter. Conduction, convection, and radiation are ways that thermal energy moves. Conduction is the flow of thermal energy between objects that are touching. Convection is the movement of warm liquids or gases to cooler areas. Radiation is the transfer of thermal energy through electromagnetic waves. We use electrical energy every day. But where do we get it? People generate electricity in many ways. All involve changing some other form of energy into electrical energy. This power plant is turning chemical energy into electrical energy. 2 3
Everyone Uses Power Picture yourself in your house during a thunderstorm. You are working on an art project while listening to the radio. Your brother is watching television. Your grandmother is in the kitchen, baking a cake. Several lights are on in the house. You notice that the storm is getting worse when you see a streak of lightning in the sky. Suddenly, the house is dark and silent. You look outside and see that the streetlights are off and all the other houses are dark too. Lightning has struck a power line and shut off the electricity in your neighborhood. Hospitals rely on electricity. They have backup sources in case the power goes out. Portable Power Cellular phones run on batteries. Batteries are a handy way of storing electricity. They let us take power wherever we go. The electricity is stored in layers of special chemicals. How many things in your household run on batteries? There is hardly anything we do that doesn t rely on electricity. We use it for light, heat, refrigeration, computer power, elevators, entertainment, and so on. Factories depend on electric power to make most of the things we use. Beauty salons, restaurants, and laundromats all need electric power to provide goods and services to customers. Most of this electricity is supplied by power plants. Power cables built over train tracks provide the trains with electricity. 4 5
Power Plants Power plants need a source of energy to produce electricity. This source of energy might be a fossil fuel such as coal, oil, or natural gas. These plants use the heat energy from burning fuel to make steam, which is used to make electricity. The movement of wind and water is a source of energy for some power plants. Others use nuclear energy or the heat of rocks deep beneath the ground. At a coal-fired power station, burning coal heats water into steam, which drives a turbine. At a hydroelectric dam, flowing water from a river is used to spin a turbine. Any of these sources of energy can be used to spin a turbine. A turbine takes kinetic energy and transfers it to a generator, which makes electricity. The kinetic energy may come from wind or moving water. Or it may come from steam made by burning fossil fuels. Turbines have many blades attached to a shaft, or rod. Kinetic energy turns the blades on the turbine, which rotates the shaft. The shaft is connected to the generator. The spinning movement of the shaft drives the generator. About 70 percent of the electricity used in the United States is produced using coal, oil, or gas as a source of energy. 20 percent is made using nuclear energy. About 7 percent is produced by hydroelectric, or water, energy. The remaining 3 percent is made by wind and other types of energy 6 7
Bicycle Generator You may have seen a tiny generator such as this on an older bicycle. It transforms the movement of the wheel into electricity, which powers the headlights. When you ride a bike with a generator, you have to turn the pedals a bit harder to provide the energy that is changed into electricity. Many power plants have several generators. Generators A generator is a machine that converts kinetic energy into electrical energy. In a power plant, a turbine spins a coil of wire inside the generator. The coil is surrounded by magnets. As the coil spins, it generates a small electric current in each section of its wire. Together these currents create a large amount of electricity. The electricity flows out of the generator to begin its journey to homes, factories, and businesses. The picture below shows a simple homemade generator. The two magnets create a magnetic field. A wire is bent into a square coil and held on a rod. The rod holds the square coil in the magnetic field and allows it to spin. As the coil spins, it creates an electric current. The current flows through the wires and into the meter, which shows how strong the electricity is. The wire and magnets in this homemade generator create an electric current. wires run under board magnets meter registers voltage wire coil spins between magnets 8 9
Electricity Supply So how does the electricity from a power plant get to homes, schools, and businesses? Transformers and wires connect power plants to all these places. First the electric current from a generator goes into a transformer. A transformer is a large machine that increases the voltage, or strength, of the electric current. When electric power is carried long distances, the voltage is increased to a very high level. Weak currents can t travel long distances efficiently. Power lines on pylons, or towers, carry the high-voltage power for hundreds of miles. Distribution Grid A distribution grid is all the wiring, transformers, and other equipment that connects a power plant to the buildings it supplies. First the electricity goes into transformers that increase its voltage. These are called step-up transformers. Then it travels through high-voltage wires. power station power lines industry homes Next the current reaches substations that contain other transformers. These are called step-down transformers because they reduce voltage. A device called a regulator bank maintains the proper voltage. Then the power is split off in different directions. Power lines carry the electricity to individual buildings. While most power lines are on poles, some are buried underground. An engineer checks the voltage at a power substation. step-up transformer pylons step-down transformer The symbol on this sign indicates high voltage. It is placed in locations to warn people of high electric voltage. 10 11
Electricity in the Home When electricity reaches a building, the voltage is decreased further. A transformer drum attached to a pole reduces the voltage for normal household use. If power lines in an area are buried underground, separate transformer boxes are used for each home. Electric power enters a house or other building through a meter. People have to pay the electric company for power. The meter keeps track of the amount of electricity used and how much it costs. Electric wires run from the meter through the walls of a building. One wire carries electricity to each light switch, outlet, or electric socket. This diagram shows the circuit of electricity in a house. Notice the meter, the fuse box, and the sockets. circuit breaker lighting circuit Electricity travels through a building in a circuit, or circular pathway. Wires travel to each room and connect to outlets. Outlets are the places where you plug in things that use electricity. Buildings are fitted with safety devices to prevent fire due to an electrical overload. Circuit breakers cut off the electricity whenever the current increases to an unsafe level. The power is turned back on by flipping a switch. In cars and some appliances, fuses do the same job as circuit breakers. Fuses burn out when too much power flows through them, stopping the flow of electricity. A dishwasher needs electricity to run. meter outlet Fuses such as these are found in appliances and cars. They must be replaced when they burn out. 12 13
Fossil Fuels Power plants need energy to produce electricity. Much of this energy comes from coal, oil, or natural gas. These resources are known as fossil fuels. Millions of years ago, much of the Earth was covered with swamps. When the plants living in the swamps died, their remains decayed and turned into a brown, spongelike matter called peat. Over time, layers of soil, rock, and volcanic ash buried the peat. Pressure and heat changed the peat into coal. Oil was formed through a similar process. This oil rig is set up over the ocean. Pipelines or ships carry the oil and gas to refineries. Open-cast mining is a way to mine coal that makes huge holes in the ground. Coal is removed from the Earth by mining. In underground mines, a series of deep tunnels reach coal beds deep in the Earth. In surface mines, layers of soil only a few feet deep are removed. Oil and natural gas are removed by drilling. Fossil fuels are widely used because they are easy to find and collect. However, fossil fuels cause serious problems. Burning coal causes smog and other forms of pollution. Oil spills damage the environment. Most scientists believe the burning of fossil fuels is damaging Earth s atmosphere. Also, fossil fuels are not renewable, so once they are used up, they can t be replaced. crude oil Fossil fuels come in liquid form (oil), solid form (coal), and gaseous form (natural gas). coal natural gas 14 15
Nuclear Power Another form of energy used to produce electricity is nuclear power. About 20 percent of the electricity used in the United States comes from nuclear power. In the 1930s, scientists learned to split atoms. They found that this process, called nuclear fission, releases huge amounts of energy. Nuclear fission was first used for weapons during World War II. After the war, scientists discovered how to use fission to make electricity. In nuclear fission, atoms of an element called uranium are split, releasing huge amounts of energy. This energy boils water to make steam. The steam turns a turbine, which causes the generator to make electricity. The steam is then cooled and recycled through the system to be used again. Nuclear power is a relatively dependable, clean, and inexpensive source of power. However, the waste from nuclear power plants must be disposed of very carefully, or else it can make people sick. Nuclear Fission When atoms are split, neutrons are released. The neutrons hit other atoms, causing them to split. It s similar to the way one bowling ball knocks down all the pins. Fission releases so much energy that only a small amount of uranium is needed. neutron nucleus nucleus splits energy A dome of concrete and steel surrounds this nuclear reactor. It allows the nuclear reaction to be used safely. neutrons 16 17
Renewable Energy As the demand for energy in the world increases, the search for renewable energy sources has become more important. The supply of fossil fuels is running out quickly. Several sources of renewable energy are used in parts of the world today. These sources include wind energy, hydroelectric energy, tidal energy, geothermal energy, and solar energy. There are both benefits and drawbacks to the use of each source. Wind power is clean, readily available, and does not harm the environment. However, since many people think that turbines are ugly or noisy, they don t want them in their neighborhoods. As a result, turbines may be placed far from areas where people live. Wind Turbines The movement of the wind turns the blades on a wind turbine. The generator at the top of the turbine changes this movement into electricity. The electricity is then sent through cables to locations where it is used. blade generator Some wind turbines work on their own, while others work in groups called wind farms. 18 19
Solar cells convert light directly into energy, without the need for turbines or generators. There are presently three tidal power plants in the world. They are located in France, the United States, and Russia. Moving water can be made into energy known as hydroelectric power. To capture this power, a dam is built across a moving river. The moving water is held back, forming a lake. The water in the lake is released through pipes to a turbine, which generates electricity. Hydroelectric power is a renewable energy source. However, it requires a rushing river, which might not be near cities that need the most electricity. Also, large land areas may have to be flooded in order to get enough water. The movement of ocean tides provides the energy used in tidal power plants. Ocean tides come in and out twice each day. At a tidal power plant, the water flowing back toward the ocean turns a huge turbine, producing electricity. Geothermal energy uses the heat deep inside the Earth. Water is pumped into hot rock underground, where it turns into steam. This steam can be used to provide heat to buildings directly. Or it can be used to drive generators that produce electricity. Geothermal energy is renewable and dependable and is not a source of pollution. However, geothermal power plants are expensive to build. Also, much of the hot rock is so deep underground that it cannot be reached with the technology available. Solar power plants change energy from the Sun into electricity. Solar energy is renewable and doesn t cause pollution. However, solar energy is not available at night or on cloudy days, so it must be stored. When it is stored, some of its power is wasted. Solar cells, or devices that change sunlight into electricity, are expensive and not very efficient. 20 21
All power plants need an energy source. Today fossil fuels produce much of our electricity. However, the use of fossil fuels has caused pollution. Also, since fossils fuels are nonrenewable, our supply will be used up in this century. Scientists are working to improve the use of other energy choices. Some scientists are trying to develop more efficient and less expensive solar cells. Others are trying to find ways to recycle uranium. Still others are working to find better ways to reach geothermal reservoirs deep in the Earth. We must find new sources of energy soon because our need for electricity is growing. We need an energy source that can give us the power we require without damaging the Earth. 22 23
Glossary circuit current fossil fuel generator geothermal energy the complete path over which an electric current flows a flow of electricity a fuel that was formed in the Earth millions of years ago from the remains of plants or animals a machine that makes electricity by turning a coil of wire inside a magnetic field power created from Earth s heat hydroelectric energy power created by using moving water nuclear fission the splitting of the nucleus of an atom to create energy What did you learn? 1. How do batteries make our lives easier? 2. What is the purpose of an electric meter? 3. What are the benefits and drawbacks of the use of fossil fuels as an energy source? 4. When electricity is transmitted from power plants to homes and other buildings, its voltage has to be increased, decreased, and regulated. Write to explain how and why this happens. Include examples from the book to support your answer. 5. Predict Based on what you learned about renewable resources, what types of energy do you predict will become more important in the future? renewable resources fuel sources that can be reused over time, such as wind, water, or the Sun solar cells turbine devices that can catch the Sun s energy and turn it into electricity a series of blades that turn a shaft, which causes the coil in a generator to rotate 24