## Acceleration of a body

Acceleration of a body is defined as-

1) The acceleration of a particle or a body is defined as the time rate of change of velocity of it i.e. Acceleration = change in velocity/time taken.

2) The acceleration of a body is change in the velocity in a unit time.

3) *Acceleration of a body* is vector quantity.

4) The acceleration of a particle or body can be positive, negative or zero.

5) A*cceleration of a body* is positive if the velocity of the body is increasing with time and is negative if the velocity of body is decreasing with time.

6) The negative acceleration is also called retardation or deceleration.

7) CGS unit of acceleration is cm/s2.

8) The dimensional formula for acceleration is [ M^{0}L^{1}T^{-2}].

9) If *acceleration of a body* is zero, then the body is moving with constant velocity.

#### Uniform acceleration

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

b) Velocity time graph of a uniformly accelerated motion is st. line inclined to time axis.

#### Variable acceleration

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

#### Average acceleration

a) 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. average acceleration = total change in velocity/ total time taken.

b) For a uniformly accelerated motion, the average acceleration is equal to uniform acceleration.

#### Instantaneous acceleration

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