**Acceleration**

If any rigid body with un-uniform speed increases its velocity continuously then the rate of the increasing speed is known as acceleration of the body. That is, increasing of the velocity in respect of time is known as acceleration.

*Def.* The rate of change of velocity of a body with respect to time is called its Acceleration.

**Let, **

Initial velocity of the body= *u*

Final velocity of the body= *v*

Time interval = *t*

Acceleration of the body = *a*

**Unit of ****Acceleration**

MKS o SI method : metre / second^{2}

CGS Method : centimeter / second^{2}

FKS Method : foot / second^{2}

**Problems:**

A car is travelling at 54 km / h. If its velocity increases to 72 km / h in 5 second, then find the acceleration of the car in SI unit.

We know, metre / second^{2 }are the unit of acceleration in SI unit.

**Retardation**

If any rigid body with un-uniform speed decreases its velocity continuously then the rate of the decreasing speed is known as acceleration of the body. That is, decreasing of the velocity in respect of time is known as Retardation.

*Def.* The rate of change of velocity of a body with respect to time is called its Retardation.

**Let, **

Initial velocity of the body= *u*

Final velocity of the body= *v*

Time interval = *t*

Retardation of the body = *a*

**Unit of ****Retardation**

MKS o SI method : metre / second^{2}

CGS Method : centimeter / second^{2}

FKS Method : foot / second^{2}

**Problems:**

A car is travelling at 72 km / h. If its velocity increases to 54 km / h in 5 second, then find the Retardation of the car in SI unit.

We know, metre / second^{2 }are the unit of Retardation in SI unit.