English: Animation of a circular orbit for Newton's theorem of revolving orbits. All three planets (red, blue and green) feel an attractive force that provides the centripetal acceleration necessary to keep them moving on the cyan circle. (This centripetal force can have any dependence on the distance r to the center.) However, due to the influence of an attractive inverse-cube center force, the green planet revolves three times as fast around the center as does the blue planet, which feels no such force. The red planet feels a repulsive inverse-cube force that exactly cancels the centripetal force, leaving it stationary on the circle.