 In Newtonian mechanics, the centrifugal force is an inertial force also called a fictitious or pseudo-force directed away from the axis of rotation that appears to act on all objects when viewed in a rotating frame of reference. The concept of centrifugal force can be applied in rotating devices, such as centrifuges, pumps, centrifugal governors, and centrifugal clutches, and in centrifugal railways, planetary orbits and banked curves, when they are analyzed in a rotating coordinate system. The term has sometimes also been used for the reactive centrifugal force that is a reaction to a centripetal force. Centrifugal force is an outward force apparent in a rotating reference frame. It does not exist when a system is described relative to an inertial frame of reference. All measurements of position and velocity must be made relative to some frame of reference. For example, an analysis of the motion of an object in an airliner in flight could be made relative to the airliner, to the surface of the earth, or even to the sun. The reference frame that is at rest or one that moves with no rotation and a constant velocity relative to the fixed stars is generally taken to be an inertial frame. Any system can be analyzed in an inertial frame and so with no centrifugal force. However, it is often more convenient to describe the rotating system by using a rotating frame. The calculations are simpler, and descriptions more intuitive. When this choice is made, fictitious forces, including the centrifugal force, arise. In a rotating reference frame, all objects, regardless of their state of motion, appear to be under the influence of a radially from the axis of rotation outward force that is proportional to their mass, to the distance from the axis of rotation of the frame, and to the square of the angular velocity of the frame. This is the centrifugal force. As humans usually experience centrifugal force from within the rotating reference frame, e.g. on a merry-go-round or vehicle, this is much more well known than centripetal force. Motion relative to a rotating frame results in another fictitious force, the Cauchy Realize force. If the rate of rotation of the frame changes, a third fictitious force, the Euler force is required. These fictitious forces are necessary for the formulation of correct equations of motion in a rotating reference frame and allow Newton's laws to be used in their normal form in such a frame with one exception, the fictitious forces do not obey Newton's third law, they have no equal hand. Opposite counterparts.