Define Instantaneous acceleration.

Explanation

Instantaneous acceleration or acceleration of a particle at time .t. is given by the ratio of change in velocity over `Deltat` as `Deltat` approaches zero.
Acceleration `veca=lim_(Deltat""to0)(Deltavecv)/(Deltat)=(dvecv)/(dt)`
In other words, the acceleration of the particle at an instant is equal to rate of change of velocity.
(i) (i) Acceleration is a vector quantity. Its SI unit is `ms^(-1)` and its dimensional formula is `[M^(0)L^(1)T^(-2)]`.
(ii) Acceleration is positive if its velocity is increasing, and is negative if the velocity is decreasing. The negative acceleration is called retardation or deceleration.