ACCELERATION, as used in mechanics, a term denoting the rate of change in the velocity of a moving body. It is what the increment in velocity in a unit of time would be if the rate of change were uniform for that unit. When a body falls in a vacuum near the earth's surface, the increment in velocity is about 32.16ft. per second, and this is known as the acceleration of gravity. In astronomy the term has other uses, as when it refers to the time which the stars gain upon the sun in passing the meridian each day. (See MECHANICS ; UNITS, DIMENSIONS, OF GRAVITATION.)