Centrifugal Homepage

Question: Why is centrifugal force not a force?

(Posted by: Heba on 2009-06-09 19:43:52)

Posted by: wjllope on 2009-06-09, 19:48:18

Nowadays, centrifugal force is most commonly introduced as a force that is observed in a rotating reference frame, and referred to as a fictitious or inertial force (a description that must be understood as a technical usage of these words that means only that the force is not present in a stationary or inertial frame).[1][2] Centrifugal force is zero when the rate of rotation of the reference frame is zero, independent of the motions of objects in the frame.[3] If objects are seen as moving within a rotating frame, this movement results in another fictitious force, the Coriolis force; and if the rate of rotation of the frame is changing, a third fictitious force, the Euler force is experienced. Together, these three fictitious forces allow for the creation of correct equations of motion in a rotating reference frame.[3] en.wikipedia.org/ wiki/ Centrifugal_force Edit: Mef - great comic - i've always loved that strip... thanks for the laugh... cheers

Posted by: Mef on 2009-06-09, 19:53:05

Typically when we describe a situation referring to centrifugal force, what we are actually referring to is centripetal acceleration. In this case, the spinning object naturally wants to hold it's course in a straight line (due to inertia), it just so happens that this straight line points away from the center of the object. Some people call this a centrifugal force (center-fleeing) because they think there's a force pushing out from the center. The actual force that you have is the force that holds the object moving in a circle--a force that points toward the center, not away from it. The acceleration of the object is always toward the center of the system, therefore the force must always be pointing to the center. So the force is in reality a centripetal force (going toward the center), NOT a centrifugal force (going away from the center).

Posted by: engineer on 2009-06-09, 20:00:23

The centrifugal "force " is really linear momentum. According to Newton's second law, objects that are moving in a straight line at constant speed want to keep doing that. An object that is being made to move in a circle is really trying to move in a straight line at all times and is being acted on at all times by an inward center-seeking (centripetal) force that makes it go in a circle. This may be the friction of tires, or tension in a string. The object's momentum makes it "feel " like some force is pushing outward when it is really a manifestation of the object's desire to keep moving in a straight line. If that centripetal force is removed, the object will immediately start moving in a straight line again.

Posted by: 00 Physicist on 2009-06-09, 20:19:16

The Centrifugal force is a force... hence the name. It is, however, a special kind of force: a pseudo force (also called fictitious, inertial, d'Alembert and so-on). The centrifugal force acts on all masses in a *non-inertial* reference frame. Using Lagrangian Mechanics the Centrifugal and Coriolis forces naturally appear, and become zero in inertial frames of reference. These kinds of forces are odd in that they do not obey Newton's Third Law --they do not arise from physical interaction, but rather the acceleration of the reference frame.

Posted by: debydete on 2009-06-09, 20:51:49

Centrifugal force is the "apparent " force observed from a non-inertial frame (i.e. rotating frame of reference). It is "apparent " because there is no visible cause for it. For example; place a ball on the front seat of your car as you travel down the highway. Now go around a curve. The ball starts from rest, from your point of view, and rolls toward the door. There is no visible force on the ball but it accelerates. 1st law is violated. This is a centrifugal force on the ball. The same phenomenon when viewed from an inertial reference frame is; the ball is simply continuing in its straight line trajectory and the car is rotating out from under the ball. There is no "real " force on the ball and the ball doesn't accelerate. 1st law is intact.