centripetal force

Centripetal force is the force applied to a body to maintain its motion in a circular path. To maintain a body of mass m moving with instantaneous velocity v in a circular path of radius r, a centripetal force of magnitude mv 2/r must be applied toward the center of the circle. If a body is moving in a rotating frame, it experiences a centrifugal force, apparently acting away from the center of rotation, numerically equal to the external centripetal force. Because, from the point of view of an observer external to the rotating frame, the centrifugal force has no real existence, it is sometimes termed a fictitious force.