What makes the wheels turn round? This simple question is asked over and over again. To reply means pages of answers and volumes of explanations.
The Water Fall.—Go with me to the little stream I have in mind, and stand on the crest of the hill where we can see the water pouring down over the falls, and watch it whirling away over the rocks below.
The world was very, very old, before man thought of using the water of the falls, or the rushing stream below, to grind his corn or to render him other service.
Water Moves in One Direction Only.—What the original man saw was a body of water moving in one direction only. When he wanted to grind corn he put it in the hollow of a rock, and then beat it with a stone, which he raised by hand at each stroke. In doing so two motions were required in opposite directions, and it took thousands of years for him to learn that the water rushing along in one direction, could be made to move the stone, or the pestle of his primitive grinding mill, in two directions.
It took him thousands of years more to learn another thing, namely, that the water could be made to turn the stone round, or rotate it, and thus cause one stone, when turning on another, to crush and grind the grain between them.
Now, as we go along with the unfolding of the great question of motors, we must learn something of the terms which are employed, to designate the different things we shall deal with, and we ought to have some understanding of the sources of power.
What Is Energy?—The running, as well as the falling water represent energy. This is something which is in the thing, the element, or the substance itself. It does not come from without. It is not imparted to it by anything.
Stored or Potential Energy.—At the top of the falls, look at that immense rock. It has been there for centuries. It, also, has energy. There is stored within it a tremendous power. You smile! Yes, the power has been there for ages, and now by a slight push it is sent crashing down the precipice. The power developed by that fall was thousands of times greater than the push which dislodged it.
But, you say, the push against the stone represented an external force, and such being the case, why do you say that power is within the thing itself? The answer is, that not one iota of the power required to push the stone off its seat was added to the power of the stone when it fell. Furthermore, the power required to dislodge the stone came from within me, and not from any outside source.
Here we have two different forms of energy, but both represent a moving force. The power derived from them is the same.