Fig. 168
235. Wheel and Axle.—The mechanical power next in simplicity to the lever is the Wheel and Axle. The most familiar applications of this power we see in drawing water and in raising heavy articles in stores. The principle of this power is the same as that of the lever, as may be shown in Fig. 168, which represents a section of the wheel and axle. The power, P, hangs by a cord which goes round the wheel, and the weight, W, by a cord around the axle. We may consider the power as pulling on a lever represented by A B, the long arm of which is A C, and the short arm B C. You see that the wheel and axle, then, may be viewed as a constant succession of levers, and it is therefore sometimes called the perpetual lever. And the same rule of equilibrium applies here as in the simple lever.
Fig. 169.
236. Windlass.—In the common windlass the power is applied to a winch or crank, D C B, Fig. 169, instead of a wheel. In estimating the power of this arrangement B C must be considered the long arm of the lever, and half of the diameter of the axle, B A, as its short arm.
Fig. 170.
Fig. 171.