**Rotational force or centripetal force**

When an object revolves in a circular path, the force that acts on the body in the direction of the centre of the circle so that it keeps the object in circular motion is called the rotational force or centripetal force. Centripetal force is a force on an object directed to the center of a circular path that keeps the object on the path.

If the centripetal force acting on a body of mass m revolving in a circular path is F and if the angular velocity of the body is ω, then in vector form it can be written as:

F = – mω^{2} ř, here ř = position or radius vector of the body with respect to its centre. Since F and ř are mutually opposite to each other, hence negative sign has been used.