Fig. 83.—The rock is easily moved.
(c) The direction of a force may be changed thus enabling work to be done that could not be readily accomplished otherwise. As, e.g., the use of a pulley in raising a flag to the top of a flag pole, or in raising a bucket of ore from a mine by using a horse attached to a rope passing over two or more pulleys. (See Fig. 84.)
(d) Other agents than man or animals can be used such as electricity, water power, the wind, steam, etc. Fig. 85 represents a windmill often used in pumping water.
A machine is a device for transferring or transforming energy. It is usually therefore an instrument for doing work. An electric motor is a machine since it transforms the energy of the electric current into motion or mechanical energy, and transfers the energy from the wire to the driving pulley.
Fig. 84.—The horse lifts the bucket of ore.
118. A Machine Cannot Create Energy.—Whatever does work upon a machine (a man, moving water, wind, etc.) loses energy which is employed in doing the work of the machine. A pair of shears is a machine since it transfers energy from the hand to the edges that do the cutting. Our own bodies are often considered as machines since they both transfer and transform energy.
We must keep in mind that a machine cannot create energy. The principle of "Conservation of Energy" is just as explicit on one side as the other. Just as energy, cannot be destroyed, so energy cannot be created. A machine can give out no more energy than is given to it. It acts simply as an agent in transferring energy from one body to another. Many efforts have been made to construct machines that when once started will run themselves, giving out more energy than they receive. Such efforts, called seeking for perpetual motion, have never succeeded. This fact is strong evidence in favor of the principle of the conservation of energy.
