Equilibrium

(lib're-ŭm,) [L., a just balance.) (Statics.) A state in which two or more forces balance each other, that is, counterpoise each other's effect, so as to leave the body at rest. Although a body supported by a fixed point is in E. whenever its centre of gravity is in the vertical line through that point (Fig. 153), the fact that the centre of gravity tends ince antly to occupy the lowest po ible position, leads us to distinguish between three states ofE.-stable, unstable, and neutral. Abody is said to be in stable E. if it tends to return to its first position after the equilibrium has been slightly disturbed. Every body is in this state when its position is such that the slightest alteration of the same olevates its centre of gravity; for the centre of gravity will descend again when permitted, and after a few oscillations the body will return to its original position. Abody is caid to be in unstable E., when after the A B Fig. 310. slightest disturbance it tends to depart still more from its original position. A body is in this state when its centre of gravity is vertically above the point of support, or higher than it would be in any adjacent position of the body. An egg standing on its end, or a stick balanced upright on the finger, is in this state. Lastly, if in any adjacent position a body still remains in equi. librium, its state of E. is said to be neutral. In this ca sean alteration in the position of the body neither raises nor lowers its centre of gravity. A perfect sphere resting on an horizontal plane is in this state. Fig. 310 represents three cones A, B, C, placed respectively in stable, unstable, and neutral E. upon an horizontal plane. The letter g in each shows the position of the centre of gravity. E. of Power. (Pol.) See BALANCE OF POWER. [s. 337]