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.

 

Centrifugal force

Centrifugal force is a force that must be included in the calculation of equilibria between forces in a spinning frame of reference, such as that of a rotating space station. In the rotating frame, the forces on a body of mass m are in equilibrium (as evidenced by the body staying at the same place) only if all forces acting on it, plus a centrifugal force mv²/r directed away from the center of rotation, add up to zero. The centrifugal force is often described as being a "fictitious force" in the sense that it is a reaction to the centripetal force needed to keep an object moving on a curved path.