Acceleration

The rate of change of velocity or speed. Velocity is steady and is measured in distance per time (e.g., feet per second, miles per hour, kilometers per hour). Acceleration keeps increasing and is measured in velocity per time (e.g., feet (or meters) per second per second or feet (or meters) per second squared). It is a vector quantity and has both magnitude and direction.
See also angular acceleration, lateral acceleration, sluggish acceleration, yaw acceleration