What is centripetal force?

For a body to move at the same velocity, in a linear
direction or a circular direction, the net force acting on it must be zero. Now for a
body that is rotating, there is a force acting away from the point around which it is
rotating. This is evident from the fact that if you try to rotate a mass tied around a
string and let go of the string, the mass flies outwards. This is due to a force called
centrifugal force.

To counter the centrifugal force another
force called centripetal force is required. This is pointed towards the center of
rotation. It is the result of differing causes, for example the gravitational force
between the Earth and the Sun provides the centripetal force in this case. For electrons
rotating around the nucleus of an atom, it is electro-magnetic attraction between the
protons and the electrons.