# Centripetal force and Centrifugal force

When a particle is moving along a circular path, it is accelerated towards the centre of the circular path. Due to this acceleration there must be force acting on the particle towards the centre and this force is known as centripetal force.

Centripetal force is defined as the force which acts towards the centre along the radius of the circular path on which the particle is moving with uniform velocity.

Let a stone be tied to one end of a string and whirled in a horizontal plane with constant speed. The stone is subjected to a force directed towards the centre of the circle. This force acting towards the centre of the circle is called centripetal force.

By Newton’s third law, there must be a reaction to this force. This reactive force which is directed away from the centre is called centrifugal force.

The centrifugal force is defined as the force acting along the radius of the circle, away from the centre, to balance the centripetal force.

The centripetal force and centrifugal force are equal in magnitude but opposite in direction. As centrifugal force is a reaction force, it ceases once the centripetal force stops.

## Examples for centripetal force

The centripetal force is responsible for circular motion. Without this force the body cannot move along a circular path. This force can be produced in different ways.

1. A body tied to one end of a string is being rotated in a circle; the centripetal force is supplied by the tension of the string.

2. The moon revolving around the earth, the centripetal force is the gravitational pull of the earth on the moon.

3. A person riding a cycle along a circular path, the necessary centripetal force is supplied by a sidewise pressure exerted by the road on the tyres.

## Examples for centrifugal force

1. A stone tied to one end of a string is being rotated in a circle, the stone itself exerts an equal and opposite force on the hand. It is due to the centrifugal force.

2. A centrifugal pump is used to pump well water on the basis of centrifugal force.