Acceleration
in natural philosophy, the rate of increase of velocity of a moving body in a unit of time. If the acceleration is uniform, as in the case of a body falling or ascending under the action of gravity, the velocity is proportional to the time, and the space moved through varies as the square of the time.
The acceleration of gravity is the increasing rate of motion with which a falling body approaches the earth , and is reckoned as a little more than 32 feet a second. Minus, or negative, acceleration is the corresponding loss of motion .
In astronomy, the secular acceleration of the moon's mean motion is an increase of about 11 seconds per century in the rapidity of the moon's mean motion. It was discovered by Halley and explained by Laplace.