If the magnitude or the direction or both of the velocity changes with respect to time, the particle is said to be under acceleration.
Acceleration of a particle is defined as the rate of change of velocity. Acceleration is a vector quantity.
Acceleration = change in velocity / time taken
If u is the initial velocity and v, the final velocity of the particle after a time t. then the acceleration.
a = (v – u)/t
Its unit is ms-2 and its dimensional formula is LT-2.
The instantaneous acceleration is, a = dv/dt = d/dt (ds/dt) = (d2s/dt2).