Principle of Centripetal and Centrifugal Forces

To maintain a body on a circular path, a force must be applied on it. This force is called centripetal force (CpF), that transmits to the body a centripetal acceleration.

CpF is not a new type of force. The nature of CpF is different in different situations, as shown in the following examples: in the case of a body tied to a string and rotated horizontally or vertically, the centripetal force is the elastic force of the string, for the Moon, which rotates around the Earth on a circular orbit, the CF is the force of gravitational attraction exercised by Earth to the Moon, for an electron that rotates around the atomic nucleus, the centripetal force is the force of attraction between the electron and the nucleus, of electrostatic nature.

Any force keeps its direction if it doesn't suffer any action from an exterior factor to change it. A roller-coaster at an amusement park, which moves along a rail, would continue to go in a straight line if the rail -which is curved - would not force it to change direction constantly. A force acting on the direction of travel keep the car on track even upside down. This force is called centrifugal force (CfF).

CpF is a force that tends to remove the body of the circular path, transmitting a movement towards the circle radius. Centrifugal force is a fictional force, it exists only for the observers located within the system which is related to the body. It is determined by body inertia and not due to mechanical interactions, so it is called completely the centrifugal force of inertia.

CpF is acting on the links. The strength that squeezes you in the cabin wall of the marry-go-round is the CfF. The force which is acting on the arm of the marry-go-round and gives it tension is the centripetal force.