The Conservation of Energy
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
p-73
2025-11-03
44
When a ball is fired from a rifle, none of the energy that is developed by the combustion of the powder is lost, but it is all transformed into other forms of energy. Both the rifle and the ball are put in motion, producing kinetic energy; the air is thrown into vibration, producing sound; the ether is thrown into vibration, producing light; and to these results must be added the heat of the combustion. The sum of all these forms of energy is equal to the potential energy of the powder, and there is no loss.
By extending the consideration to all kinds of transformation of energy, scientists have reached the conclusion that energy can neither be created nor destroyed, and hence that the total amount of energy in the universe is constant.
The pile driver is a good example of both the transformation and the conservation of energy. As the head rises from the top of the pile the work of the engine gives it potential energy. The measure of this is the amount of work it is capable of doing. This is changed into kinetic energy as the head falls, and when it strikes the top of the pile it delivers the same amount of kinetic energy that it had of potential energy when it started. That is, its kinetic energy equals its potential energy. A simple way to compute kinetic energy is to find how far the velocity of the moving body would carry it vertically upward and use that distance for h in the expression for potential energy.
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