What is centripetal force? From where does the moon get the centripetal force required for its motion around the earth?
Centripetal force:
i) When a body moves along a circular path with a uniform speed, its direction of motion changes at every point.
ii) The change in direction involves change in velocity or acceleration. The force that provides this acceleration and keeps the body moving along the circular path, acts towards the centre. This force is called centripetal (centre seeking) force.
iii) Therefore, a force which is required to make a body move along a circular path with uniform speed is called centripetal force.
iv) Centripetal force always acts along the radius and towards the centre of the circular path.
v) The figure given below shows that it is the centripetal force which continuously deflects a particle from its straight line path to make it move along a circle. 
Fig. Centripetal force.
Example:
The moon needs a centripetal force, for its circular motion around the earth. This centripetal force is provided by the gravitational attraction exerted by the earth on the moon.
