- Books Name
- Science Made Easy Science Book

- Publication
- Science Made Easy

- Course
- CBSE Class 9

- Subject
- Science

**Acceleration - **

Acceleration is seen in non-uniform motion and it can be defined as the rate of change of velocity with time.

Acceleration (a) = Change in velocity/Time = (v-u)/t

where, v = final velocity, u = initial velocity

If v > u, then ‘a’ will be positive (+ve).

**Retardation/Deceleration - **

Deceleration is seen in non-uniform motion during decrease in velocity with time. It has same definition as acceleration

Deceleration (a') = Change in velocity/Time = (v-u)/t

Here, v < u, ‘a’ = negative (-ve).

It is a vector quantity.

SI unit – m/s^{2 }( meter per second square)

**Example 1**: A car speed increases from 40 km/hr to 60 km/hr in 5 sec. Calculate the acceleration of car.

**Example 2**: A car travelling with a speed of 20 km/hr comes into rest in 0.5 hrs. What will be the valu of its retardation?

**EXAMPLE 3** : If the velocity of the car reduced to 80 m/s from 120 m/s in 8 seconds on applying breaks . Calculate its acceleration