Acceleration indicates the rate of change of the objectâs velocity (v G); i.e., the acceleration tells you how fast the objectâs velocity is changing. The component of the acceleration that is parallel to the velocity (a || G) indicates the rate of change of the objectâs speed. If a || Gis parallel to the velocity, then the object is speeding up; if a || is anti-parallel to the velocity, then the object is slowing down.