## Concept of Centripetal Force:

• It is a force acting on a particle performing circular motion, which is acting along radius of a circle and directed towards the centre of circle.
• Explanation:
If ‘m’ is the mass of the particle performing circular motion then magnitude of centripetal force is given by
Centripetal force = mass ´ centripetal acceleration.
• It is vector quantity and always directed towards centre of circle. In vector form

### Characteristics of Centripetal Force:

1. It is real force because it is provided by gravitational, electromagnetic or nuclear interaction.
2. It arises in inertial frame of reference or it arises in a frame of reference moving with constant velocity or with acceleration zero.
3. It is always directed towards the centre of circular path.
4. Without it the circular motion is not possible.
5. Work done by it is zero.
6. In vector form

### Examples of Centripetal Force:

1. When a stone tied to one end of a string is whirled horizontally, there is an inward force exerted by the string on the stone called tension. This force provides necessary centripetal force for circular motion.
2. When a vehicle moves around a horizontal circular road, the centripetal force for circular motion is provided by the frictional force between the road and the wheels.
3. In an atom, an electron moves around the nucleus in an orbit. The centripetal force required for the motion of the electron is provided by the electrostatic force of attraction between oppositely charged electrons and protons.
4. Satellite revolves around the earth in circular orbit. Necessary centripetal force is provided by the gravitational force of attraction between satellite and earth.
5. When a coin is kept on rotating disc necessary centripetal force is provided by friction between the coin and the surface of the rotating disc.
6. When a body is performing looping a loop, at the highest point of the vertical circle, necessary centripetal force is provided by the weight of the body.
7. In a circus, when the motorcyclist moves in a vertical circle in the sphere of death, at the highest point of the vertical circle, necessary centripetal force is provided by the weight of the motorcycle and motorcyclist.