Acceleration is the rate at which objects increase their velocity. It is a vector which has a direction and a size of force. It can be calculated by the following formula:

acceleration = change in velocity / time taken = (final velocity - initial velocity) / time taken

Or simply a = (v2-v1) / t, where a = acceleration, v2 = final velocity, v1 = initial velocity and t = time.

The unit of acceleration is measured in m/s² (read as meters per second second squared). If the acceleration has a negative value, then it is called deceleration.