# Centripetal versus centrifugal

#### mitch bass

can someone please compare and contrast the phenomenon of the centripetal force versus the centrifugal force.

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#### Janus

Staff Emeritus
Gold Member
Originally posted by mitch bass
can someone please compare and contrast the phenomenon of the centripetal force versus the centrifugal force.
First off, there is no such animal as the Centrifugal force or the Centripetal force, there are merely centrifugal and centripetal forces.

Centrifugal means " to flee the center" and Centripetal means "to seek the center"

They are just terms used to decribe whether any given force acts towards or away from a center.

#### HallsofIvy

Homework Helper
Imagine swinging a rock on a rope. A moving object tends to move in a straight line. In order to make the rock move out of a straight line into a circle, you have to keep pulling on the rope: that "cetripetal" force.

Of course, you hand feels the rope pulling back on it ("equal and opposite reaction"). That's "centrifugal" force.

Centripetal force is always directed toward the center of the curve, centrifugal force is always directed away from the center.

#### Hyperreality

Centrifugal force is a "fictitious force", hence it is not really a force.

Imagine if a person is on a Merry-go-around spinning. He would feel a "force" that is pulling him away from the Merry-go-around, therefore he has to hold on to the bar on the Merry-go-around enable to stay on, the force that he is exerting on the bar is acting directly inwards with respects to the center of the Merry-go-around, and this force is what we called a "centripetal force". Now imagine the person releases his grip on the bar, and got pull off by this "mysterious force" off the Merry-go-around. An observer that is on the same Merry-go-around, would see that the person is flying "radially" away from the Merry-go-around. But if there is an observer on the ground in a stationary reference frame, he would see this rather differently, he would see the person instead of flying radially, he would see him flying away from the Merry-go-around "tangetially".

People who have done physics knows that the veloctiy vector is always at right angle to the centripetal force, we can therefore say, from the viewpoint of the observer in a staionary non-rotational reference frame that the person is really flying away from the Merry-go-around due to his inertia, because inertia is the resistance of change in motion, in this case, the person's inertia has overcame the centripetal force, and thereby he will fly tangetially away from the Merry-go-around.

The reason that centrifugal force is called a fictitious force is because that it only agrees with the definition of a force (a push or a pull) when the observer is in the same rotating reference frame as the obejct; while an observer in an non-rotational stationary reference frame does not need to be equiped with the concept of centrifugal force. The existnce of centrifugal force is really a matter of fact that which frame of reference that the observers are in.

#### Sting

Hyperreality beat me to it, but there is no centrifugal force.

That force is really the tangential velocity "pushing" an object away from the center.

Just some repetitive info.

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