More on Centrifugal/Centripetal Force....

This discussion probably has very little to do with a discussion of skiing, but it seems to raise its ugly head on a regular basis! Understanding the nature of these forces is an interesting quest, but the fact is that our bodies know all they need to know about the phenomena, from a lifetime of experience dealing with gravity, other forces, acceleration, and inertia. So it's an intellectual game only, unless we draw false conclusions of what "should be" based on false notions of what "is"!

Here is a short and fairly clear explanation of Centrifugal and Centripetal forces, from

Grolier's Interactive Encyclopedia:

<BLOCKQUOTE>quote:</font><HR>centrifugal and centripetal forces

{sen-trif'-uh-gul, sen-trip'-uh-tul}

Centripetal ("center-seeking") force is the radial force required to keep an object continually diverted in its path so that it travels in a circle. When a ball on a string is swung in a circle, the string supplies the centripetal force. If the string breaks, the ball will move in a straight line tangential to the original circle. In satellite motion, gravitation between the parent body and the satellite supplies the centripetal force.

When a car goes around a curve, the friction between tires and road must sustain sufficient sideways force to provide the necessary centripetal force for curved motion. Properly constructed roads are banked on curves, so that a small component of the road's reaction to the car's weight is directed horizontally toward the center of the turn, supplying the centripetal force. Passengers in a car going around a curve are not subject to external frictional forces and in their reference frame experience an outward, centrifugal force. Centrifugal ("center-fleeing") force refers to the same phenomenon as centripetal force but is the force experienced by a circling object as observed from the rotating frame of reference.

Some physicists prefer to think of forces that arise because of acceleration of the reference frame as pseudoforces. A consistent description of resulting motion can be obtained in either the moving or stationary reference frame, however, as long as the two are not confused. It is not appropriate, for instance, to think of the centrifugal force as the equal but opposite reaction to the action of the centripetal force.

The magnitudes of the two forces are the same, and equal to mv2 /r where m is the mass of the circling object, v is its speed, and r is the radius of the circular path. Expressed in terms of angular frequency in radians per second, omega, frequency in revolutions per second, f, or period, T, the centripetal force is also equal to momega2r, 4pi2mf2r, and 4pi2mr/T2. Because the radial direction of the force is always perpendicular to the tangential velocity, the force does no work on the object.

The centrifugal force experienced in a rotating system is proportional to mass; therefore, rotating systems can create gravitationlike conditions. In space, for instance, people could live comfortably with normal apparent weight on the inside of rotating structures. For them, "down" would be in the outward radial direction.

C. E. Swartz

Bibliography: Ohanian, H. C., Principles of Physics (1993). <HR></BLOCKQUOTE>

Grolier's description alludes to different "frames of reference," including "stationary" and "moving" frames of reference, as well as the frame of reference of the astronauts in the rotating space station (for them, centrifugal force pulls straight "down"--indeed, it DEFINES "down"--and substitutes for the "real" force of gravity). The discussion of various frames of reference, based on the reality that all motion is relative (things only move or remain stationary relative to other things), can get quite intersting! But to really understand the nature of centrifugal force, it can be an illuminating journey!

Best regards,

Bob Barnes

<FONT COLOR="#800080" SIZE="1">[ November 10, 2001 11:57 AM: Message edited 1 time, by Bob Barnes/Colorado ]</font>