Acceleration

(1) Rate of change in the velocity of any moving body. A number of units of length in one unit of time, and the difference between the velocity observed at the end of one unit of time and the velocity at the end of the next succeeding unit. Where this difference is negative, the motion is being retarded. Acceleration may be uniform or varied. The most usual of the uniform accelerations is that due to gravity, which produces a change of velocity of 32.2 feet per second when a body falls or is thrown upward into the air. There are also astronomical accelerations observed in the motions of the heavenly bodies-due, for the planets and fixed stars, to the orbital motion of the members of the solar system; the apparent acceleration of the moon has not been fully explained. (2) Occurrence of the stages of development of an animal earlier and earlier in its life history as the generative cycles are repeated; e.g., the lower Crustacea hatch as free swimming Nauplius larvæ, while in the higher this stage is pa ed in the egg, the free larva here corresponding with the adults of lower forms. See DEVELOPMENT.