The Lever and the Pulley.—If we should substitute a lever (D) for the pulleys, the similarity to the lever ([Fig. 127]) would be apparent at once. The pivot (C) in this case would act the same as the pivot (C) in the lever illustration.
In the same manner, and for like reasons, the[p. 133] wedge, the screw and the incline plane, are different structural applications of the principles set forth in the lever.
Whenever two gears are connected together, the lever principle is used, whether they are the same in size, diametrically, or not. If they are the same size then no change in power results; but instead, thereof, a change takes place in the direction of the motion.
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| Fig. 129. | Fig. 130. |
| Change of Direction[ToList] | |
When one end of the lever (A) goes down, the other end goes up, as shown in [Fig. 129]; and in [Fig. 130], when the shaft (C) of one wheel turns in one direction, the shaft of the other wheel turns in the opposite direction.
It is plain that a gear, like a lever, may change direction as well as increase or decrease power. It is the thorough knowledge of these facts, and their application, which enables man to make the wonderful machinery we see on every hand.
Sources of Power.—Power is derived from a[p. 134] variety of sources, but what are called the prime movers are derived from heat, through the various fuels, from water, from the winds and from the tides and waves of the ocean. In the case of water the power depends on the head, or height, of the surface of the water above the discharging orifice.
Water Power.—A column of water an inch square and 28 inches high gives a pressure at the base of one pound; and the pressure at the lower end is equal in all directions. If a tank of water 28 inches high has a single orifice in its bottom 1" x 1" in size, the pressure of water through that opening will be only one pound, and it will be one pound through every other orifice in the bottom of the same size.