# acceleration

Acceleration is the rate at which the velocity of an object
changes with time. Acceleration is a vector quantity and may involve a change in an object's speed or direction or both. **Deceleration** is considered to be negative acceleration.

For a body moving in a straight line with constant acceleration *a*,
from initial speed *u* to final speed *v*, the acceleration
is given by

*a* = (*v* - *u*)/*t* = (*v*^{2} - *u*^{2})/2*s*

where *t* is the time taken and *s* is the distance covered.

If the acceleration is not constant it is given by *dv*/*dt* = *d*^{ 2}*s*/*dt*^{ 2}.

**Linear acceleration** occurs when the rate of motion (speed)
along a straight line changes. **Centripetal acceleration** occurs in circular motion at constant angular
velocity as the direction of motion changes. Angular
acceleration occurs in circular motion when the rate of rotation changes.

Acceleration is the result of a (net) force (*F*) applied to an object (of mass *m*). We can therefore
express acceleration in terms of an applied force through this equation
derived from Newton's second
law: *a* = *F*/*m*.

The SI unit for acceleration is meter per second squared (m/s^{2}).