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ENERGY The term energy comes from energeia, the Greek word for "work." Energy is defined as the capacity to do work. Energy cannot be created or destroyed, but it can change form. Heat, light, and electricity are forms of energy. Other forms include mechanical, chemical, and nuclear energy. You can feel heat and see light, but most energy, like electricity, is invisible. We only see the result-like the lighting of a bulb. All of the forms of energy we use come from the energy stored in natural resources. Sunlight, water, wind, petroleum, coal, and natural gas are natural resources. From these resources, we get heat, electricity, and mechanical power to run machines. IT STARTS WITH THE SUN Most of our energy traces its source to the Sun. Inside the Sun, hydrogen atoms join together and become helium. This process releases energy that radiates into space in the form of waves. These waves give us heat and light. Energy from the Sun is stored in plants and animals that we eat. Long before humans existed, these ancient plants absorbed the Sun's energy, and animals ate the plants as well as smaller animals. After the plants and animals died, they got buried deeper and deeper underground. After millions of years, they turned into coal and petroleum-what we call fossil fuels-that we are so dependent on today, see WHY DO PLANTS NEED SUNLIGHT?. HOMEWORK HELP: The different forms of energy fall into two main categories. It helps to try and picture each one: Kinetic Energy is the energy of objects in motion. Water in a river, electricity in a wire, and a sled going down a hill are good examples. Potential Energy is the energy of objects that are not moving-but could move. If you stretch a rubber band and hold it, it has potential energy. Let it go and its potential energy changes to kinetic energy with a snap! Natural gas, coal, and food are other examples of potential energy. Title: ENERGY Source: World Almanac for Kids, The Date: January 1, 2006 Reading Level (Lexile): 790L Copyright (c) 2006 The World Almanac for Kids by PRIMEDIA Reference Inc. The World Almanac for Kids and Facto the Factosaurus are registered trademarks of PRIMEDIA Reference Inc. Record Number: 1108BBD494D00295