#### What is energy used for? What is energy and the importance of energy. What is the meaning of force, resistance and work, what are the differences?

To define energy, scientists must use some ideas. The first of these ideas you already have. It is the idea of force.

Every time you pick up a book, pedal your bicycle, open a door, or write your name, you are using a force. If you think about all the times when you use a force, you will find that you do one of two things: You either push something or pull it. So a force is a push or a pull. Whenever you make something move, you exert a force. But you may also exert a force without making anything move. You have probably pulled or pushed some heavy object without being able to budge it. Whether the object moves or not, you are exerting a force just the same.

Besides the force you exert with your muscles, there are other forces acting around you all the time. If you stand in an open place on a windy day, you can feel the force of the wind, or moving air. If you walk into a swift stream of water, the force of the moving water may throw you off your feet. If you step off a box or a chair, the force of gravity pulls you down. If you make a deep dive, you can feel the force of the water above you pressing on your body. You know that a magnet exerts a force on iron and steel and makes them move. Whenever anything moves, a force has been used to start it moving.

Another idea that scientists must use in defining energy is the idea of work. Work is a common word, and you may think that you know very well what it means. Work to you is probably something that you have to do but do not enjoy doing. However, like many other words, work has more than one meaning. When scientists use this word, they have a special meaning for it.

If you push as hard as you can against a table but do not move it, you have exerted a force. However, you have done no work according to a scientist. But if you move the table, you have done work. In other words, to a scientist work is done only if something is moved. You might struggle for an hour trying to move a big stone. If you could not move it, a scientist would say that you had done no work. But if you quickly brushed a tiny leaf aside, he would say that you had done work, because the leaf was moved.

When you lift a chair, climb the stairs, push a lawn mower, or drive a nail, you are also doing work. You exert a force and move something. To make it move, your force must overcome an opposing force. That is, some other force always acts against the force that does the work. This opposing force is called the resistance. Scientists use this word to define work. They say that work is done when a force overcomes a resistance and moves something.

Scientists say that energy is the ability to do work. Anything has energy if it can move something that resists being moved. In other words, if a thing has energy, it can do work. To say that something can do work is really just anotlıer way of saying that it has energy. As you can see, energy and work are closely related ideas. Whenever work is done, energy is used to exert a force that overcomes a resistance and moves something. Without energy, there would be no force and no work could be done.

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