How is one form of energy change into another? What are the energy forms and their changes.
Before people discovered how to use the other forms of energy that were everywhere around them, they did all their work with the energy of their muscles or the muscles of animals. Of course, much work is still done with muscular energy. But whenever we can, we make our work easier by using tools and other machines instead of our bare hands. To make our work even easier, we harness various forms of energy with mechanical devices such as windmills, water wheels, and steam or gasoline engines. All these devices change some form of energy into another form that can be used to run our machines. So the energy that we get from these devices is called mechanical energy.
Heat is a form of energy which causes many physical and chemical changes in matter. It makes most materials expand, and it changes water into steam. It also makes materials hot enough to burn. Another form of energy that you know about is the energy of electric current. Electrical energy provides us with light and heat. It starts our automobiles and explodes the gasoline to make them run. It operates our telephones and radios. And along with magnetism, another form of energy, it drives the electric motors in fans, vacuum cleaners, and mechanical refrigerators. Sound is still another form of energy, though we do not usually think of it as doing work. Yet, as sound passes through the air, it must overcome the inertia of the air molecules and set them in motion.
Light is different from the forms of energy that you have studied so far. It can leave the material from which it comes, shoot through space or through air, and cause changes in matter nearby or far away. The light from the sun shoots across 93 million miles of space to the earth, where it helps us see, provides green plants with the energy to make food, and causes other changes in matter. Because light moves out in all directions from its source, we say that it radiates. Radiate means spread out from the center in straight lines, or rays. There are other varieties of energy that act like light, but we cannot see them. You have probably heard or read about radio waves, X rays, ultraviolet rays, and infrared rays. All these varieties of energy that radiate through space are really parts of one form that scientists call radiant energy. Light is just the variety of radiant energy that we can see.
Another form of energy is stored in the molecules of some materials. We call this form chemical energy, because a chemical change is needed to set it free. Coal, gasoline, and all other fuels have chemical energy stored in them. When any fuel is burned, or oxidized, the stored energy is released during the chemical change. Gunpowder, dynamite, and other explosives all contain chemical energy. So do some kinds of food. As these are oxidized in our cells, the stored energy is released. We use this energy to move our bodies and keep them warm. Huge amounts of still another form of energy are locked up in the atoms of which molecules are made. Scientists discovered how to release atomic energy about twenty years ago.
Each form of energy can make things happen to matter. That is, it can make matter move or change in some way. But as matter is changed, the form of the energy is usually changed, too.
1. Ruba coin rapidly back and forth on your sleeve. What change of energy takes place in the coin?
2. Light a match. What changes of energy are taking place in the burning match?
3. Pour not more than an inch of water into the test tube and set the stopper in loosely. KEEP THE STOPPER POINTED A W AY FROM YOURSELF AND EVERYONE ELSE. Heat the water until it boils. What happens to the stopper? What changes of energy took place?
4. Set a small piece of lead on a large piece of iron or steel. Hammer the lead vigorously for a minute or two. Touch the lead with your finger. What change of energy has taken place?
5. Connect a strip of tin foil or a piece of fine iron wire to the two binding posts of a dry cell. What changes of energy take place?
6. Connect a small electric motor to two dry cells as shown in the picture. What changes of energy take place?
Under the proper conditions, each form of energy can be transformed, or changed into another form. When radiant energy from the sun strikes the earth, much of it is transformed into heat energy. But some of it is changed into chemical energy and stored in the food made by green plants. When this food is oxidized in our bodies, the chemical energy is transformed into muscular energy and heat energy. Fuels also contain chemical energy. If fuel is burned in a fireplace, the chemical energy is changed into heat. Then some of the heat energy is transformed into radiant energy. When it strikes your skin and clothes, it is changed back into heat. The chemical energy stored in a dry cell can be changed into electrical energy. And this, in turn, can be transformed into heat, light, or mechanical energy. Atomic energy can be transformed into heat energy. And mechanical energy can be transformed into electrical energy. All these transformations of energy and many others are going on around us all the time.