Lever

—A bar of metal, wood, or other substance, used to exert a pre ure, or sustain a weight, at one point of its length, by receiving a force or power at a second, and turning at a third on a fixed point called a fulcrum. Tt is usually named as the first of the six mechanical powers. There are three kinds of levers, viz.: (1) Those in which the fulcrum lies between the points at which the force and weight act; (2) those in which the weight acts at a point between the fulerum and the force; and (3) those in which the force acts ata point between the weight and the fulcrum. The distances between the fulcrum and the weight and force are called the arms. The relation between the force exerted or the pull, P, and the weight lifted or resistance overcome, W, is expre ed by the equation: PXa=W Xb in which, a is the lever arm of P, and b is the lever arm of W.