/ak sel'euh ray"sheuhn/, n.1. the act of accelerating; increase of speed or velocity.2. a change in velocity.3. Mech. the time rate of change of velocity with respect to magnitude or direction; the derivative of velocity with respect to time.[1525-35; < L acceleration- (s. of acceleratio). See ACCELERATE, -ION]
* * *Rate of change of velocity.Acceleration, like velocity, is a vector quantity: it has both magnitude and direction. The velocity of an object moving on a straight path can change in magnitude only, so its acceleration is the rate of change of its speed. On a curved path, the velocity may or may not change in magnitude, but it will always change in direction, which means that the acceleration of an object moving on a curved path can never be zero. If velocity is stated in metres per second (m/s) and the time interval in seconds (s), then the units of acceleration are metres per second per second (m/s/s, or m/s2). See also centripetal acceleration.
* * *▪ physicsrate at which velocity changes with time, in terms of both speed and direction. A point or an object moving in a straight line is accelerated if it speeds up or slows down. Motion on a circle is accelerated even if the speed is constant, because the direction is continually changing. For all other kinds of motion, both effects contribute to the acceleration.Because acceleration has both a magnitude and a direction, it is a vector quantity. velocity is also a vector quantity. Acceleration is defined as the change in the velocity vector in a time interval, divided by the time interval. Instantaneous acceleration (at a precise moment and location) is given by the limit of the ratio of the change in velocity during a given time interval to the time interval as the time interval goes to zero (see analysis: Instantaneous rates of change (analysis)). For example, if velocity is expressed in metres per second, acceleration will be expressed in metres per second per second.
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