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Revision as of 07:12, 8 May 2009 by FDT (talk | contribs) (FyzixFighter, I've already cited Nelkon & Parker)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff)In everyday understanding, centrifugal force (from Latin centrum "center" and fugere "to flee") represents the effects of inertia that arise in curved motion and are experienced as an outward force away from the center of curvature of the path or away from a center of rotation. Centrifugal force is not restricted to circular motion, however.
This article summarizes several related but distinct concepts related to the general idea of centrifugal force.
- Centrifugal force (rotating reference frame) – a fictitious force that acts on any mass in a (non-inertial) rotating reference frame.
- Centripetal force – a force pulling an object into a curved path; this force on the object is directed inward, toward a center of curvature.
- Reactive centrifugal force – according to Newton's third law of "action and reaction", the reaction force upon the object supplying a centripetal force is the reactive centrifugal force, the outward force felt by that object when it is pulling or pushing another object into a curved path.
The fictitious centrifugal force and the reactive centrifugal force are compared in the table.
| Reactive centrifugal force | Fictitious centrifugal force | |
|---|---|---|
| Reference frame |
Any | Only rotating frames |
| Exerted by |
Bodies moving in circular paths |
Acts as if emanating from the rotation axis, but no real source |
| Exerted upon |
The object(s) causing the curved motion, not upon the body in curved motion |
All bodies, moving or not; if moving, Coriolis force also is present |
| Direction | Opposite to the centripetal force causing curved path |
Away from rotation axis, regardless of path of body |
| Analysis | Kinematic: related to centripetal force |
Kinetic: included as force in Newton's laws of motion |
Reactive centrifugal force
Main article: Reactive centrifugal forceIn circular motion, the reactive centrifugal force is a real force applied by the accelerating body that is equal and opposite to the centripetal (inward) force that is acting on the accelerating body. This perspective originated with Isaac Newton in the 17th century and it appeared in textbooks up until the 1960s.
Fictitious force in a rotating reference frame
Main article: Centrifugal force (rotating reference frame)From the viewpoint of an observer in a rotating reference frame, centrifugal force is an apparent, or fictitious, or inertial, or pseudo force that seems to push a body away from the axis of rotation of the frame and is a consequence of the body's mass and the frame's angular rate of rotation. It is zero when the rate of rotation of the reference frame is zero, independent of the motions of objects in the frame.
Other topics
The concept of centrifugal force in its more technical aspects introduces several additional topics:
- Reference frames, which compare observations by observers in different states of motion. Among the many possible reference frames the inertial frame of reference are singled out as the frames where physical laws take their simplest form. In this context, physical forces are divided into two groups: real forces that originate in real sources, like electrical force originates in charges, and
- Fictitious forces that do not so originate, but originate instead in the motion of the observer. Naturally, forces that originate in the motion of the observer vary with the motion of the observer, and in particular vanish for some observers, namely those in inertial frames of reference.
Centrifugal force has played a key role in debates over relative versus absolute rotation. These historic arguments are found in the articles:
- Bucket argument: The historic example proposing that explanations of the observed curvature of the surface of water in a rotating bucket are different for different observers, allowing identification of the relative rotation of the observer. In particular, rotating observers must invoke centrifugal force as part of their explanation, while stationary observers do not.
- Rotating spheres: The historic example proposing that the explanation of the the tension in a rope joining two spheres rotating about their center of gravity are different for different observers, allowing identification of the relative rotation of the observer. In particular, rotating observers must invoke centrifugal force as part of their explanation of the tension, while stationary observers do not.
References
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