Circular Motion

The revolution of the Earth around the Sun, rotating fly wheel, electrons revolving around the nucleus, spinning top, the motion of a fan blade, revolution of the moon around the Earth etc. are some examples of circular motion. In all the above cases, the bodies or particles travel in a circular path. So, it is necessary to understand the motion of such bodies.

When a particle moves on a circular path with a constant speed, then its motion is known as uniform circular motion in a plane. The magnitude of velocity in circular motion remains constant but the direction changes continuously.

Let us consider a particle of mass m moving with a velocity v along the circle of radius r with centre O. P is the position of the particle at a given instant of time such that the radial line OP makes an angle with the reference line. The magnitude of the velocity remains constant, but its direction changes continuously. The linear velocity always acts tangentially to the position of the particle (i.e) in each position, the linear velocity is perpendicular to the radius vector .

Centripetal force

According to Newton's first law of motion, a body possesses the property called directional inertia (i.e) the inability of the body to change its direction. This means that without the application of an external force, the direction of motion can not be changed. Thus when a body is moving along a circular path, some force must be acting upon it, which continuously changes the body from its straight-line path.

Examples

Any force like gravitational force, frictional force, electric force, magnetic force etc. may act as a centripetal force. Some of the examples of centripetal force are :

• In the case of a stone tied to the end of a string whirled in a circular path, the centripetal force is provided by the tension in the string.

• When a car takes a turn on the road, the frictional force between the tyres and the road provides the centripetal force.