# Science Site

## What is Centripetal Force?

Stone sling as an example of centripetal force

In Egypt, during the days of Pharaohs, the military men used slings to throw stone or clay projectiles to harm their enemies fatally. The ends of the sling are held firmly in one hand while the projectile that is to be thrown is placed firmly over the other end. The user then swings the sling till it gains enough speed and the stone can be thrown with force. The force that drives the projectile out is a fictitious force called the centrifugal force. The force that keeps the projectile rotating in the circle is called centripetal force.

### Directed towards the center

Centripetal force acts on an object moving in a circular motion and is directed towards the center of the circular path. An object undergoing a uniform circular motion will experience this force acting on it as it moves in the circle. The centripetal force will act along the radius of the circle drawn from the location of the object on the circumference of the circle to the center.

### Magnitude of centripetal force

The amount of force in terms of the standard unit of force, Newton, depends on the speed at which the object is going round in a circle. The more the speed at which the object is moving, the more will be the centripetal force which acts on it to keep it moving in a circular motion. The force also depends on the mass of the object that undergoes such a motion. If the mass is more, the object will tend to fly away in a straight line and so the centripetal force increases in proportion to prevent the object from getting any ideas and flying off. The centripetal force also depends on the radius of the circle in which the object is moving. The bigger the radius, the lesser will be the centripetal force required to keep the object in circular motion.

### Satellite, the guiding light

It is important to understand centripetal force for a number of reasons, one of which is the weight that an artificial satellite can be allowed to bear if it were to move around the Earth collecting important information. In the case of a satellite, the gravitational pull of the Earth provides the required centripetal force. If the speed of the satellite is too high the satellite will not stay in orbit and it will fly off away from the Earth in a tangential line. On the other hand, if the speed is too low the satellite will come crashing down on the Earth.

### The fictitious force

Centrifugal force is a fictitious force and it has the same magnitude as the centripetal force but acts in the opposite direction. A fictitious force does not really exist but its effect can be felt when the observer is observing the motion from the frame of reference of the revolving object. That’s why when you are on a merry-go-round you feel that you are being thrown away. That is centrifugal force at play. There are various applications of centrifugal force as well. In laboratories, a centrifuge is used in order to separate two immiscible entities.