Linda Umbergr age 13, of Cincinnati, Ohio, for her question;

Why is heat called energy?

In everyday talk, energy is the force we use to work and play. We say that we have no energy to run to school or wash the dishes, or we say that we are so full of energy   or full of beans   that we can run a mile or dance a jig. When the mile is run or the jig is danced we are tired. The energy is all used up, the beans all gone.

Energy, it seems, is the force which gets things done, and so it is. But there are other forms of energy besides the kind we use up when our bodies are active. There is energy, or working powers in a falling stone, in a sunbeam: in soap suds and in a radio transmitter. All these things use forms of energy to cause changes or get things done.

Until about fifty years ago,, it was though that heat was a kind of fluid which was present in all hot or warm objects, As hot things cooled, it was thought, this fluid flowed out into other objects and the surrounding air. Then it was discovered that heat itself is a form of energy   it causes changes and gets things done.

It was found that heat is a form of motion and that this motion of heat is energy. More of the puzzle was solved when it was learned that the motion, or energy, of heat took place among the minute atoms and molecules of which all substances are made.

Maybe you thought that the atoms which make up an iron poker are stiff and still. Not at all. The poker is held in shape by the attraction of the iron atoms for each other. Hut even when solid„ or frozen, the iron atoms move about to some extent.

But when the iron is heated, these atoms begin to move faster and fasterat the melting point of iron they are moving fast enough to break the strong attraction which held them in solid formation.

The stiff iron bends, droops, and finally melts into a liquid.    Water is in its liquid state at ordinary temperatures, When heated its molecules speed up and fly off into the air as steam.

The hotter an object becomes, the faster its tiny atoms and molecules are chasing around. The colder an object becomes, the slower its atoms and molecules are able to move. There is still some heat, or moving energy, in a piece of ice. But if its temperature is lowered still mores there would come a time when all its heat energy would go and its tiny molecules remain perfectly still, at this low temperature there would be no motion among the molecules no heat and no energy.