Define the forms

(a) Acceleration, (b) Retardation, © Variable accelaration, (d) Average acceleration, (e) Uniform acceleration, (f) Instantaneous acceleration.

Acceleration : It is defined as the ratio of change in velocity & the corresponding time taken by the mirror object i.e.

It is vector quantity.

It is either positive or negative.

Negative acceleration is Retardation.

Unit-m/s2 in SI & cm/s2 in CGS system.

Uniform acceleration. An object is said to be moving with a uniform acceleration if its velocity changes by equal amounts in equal intervals of time.

Variable acceleration. -

An object is said to be moving with a variable acceleration when its velocity changes by unequal amounts in equal intervals of time.

The velocity time graph of a body having variable acceleration is represented by a curve.

Average acceleration. When an object is moving with a variable acceleration, then the average acceleration of the body is defined as the ratio of the total change in velocity during motion to the total time taken, i.e

(iv) Instantaneous acceleration:

(a) If a body is moving with a variable acceleration, then the acceleration of a body at the given instant of time is called instantaneous acceleration.