The Science of Energy

When you play a sport such as basketball, food energy stored in your muscles is constantly being converted into the movement energy you need to run and to throw the ball. You pass some of that energy on to the ball when you shoot, while some of the energy is lost from your body as heat.

Energy comes in different forms and can be switched from one form to another. Two forms have been mentioned already, chemical energy—part of what is called internal energy —stored in substances, and movement energy. How many more can you think of? Light, sound, heat and electricity are all forms of energy. The string of a bow pulled tight is storing energy, called potential energy , which is converted to movement energy in the arrow when the string is released.

The peoples of the ancient world didn’t think in terms of abstract ideas like energy when they thought about the way the world worked. They used gods and other mythical beings to explain why things behave as they do. The word energy , in the sense we understand it now, was first used in the 1840s by William Thomson. We will be meeting him later in the story. However, the early Greek philosophers had some interesting ideas and we turn to them first to begin our exploration of energy.

When the archer pulls back the bowstring chemical energy stored in the archer’s arm muscles is converted into potential energy in the stretched string. When the archer lets go of the string the potential energy is suddenly changed into movement energy, which is passed on to the arrow, making it fly towards the target.

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