Physics FAQs and Topic Writeups: THREAD UNDER CONSTRUCTION

[Shrike]

There is no such thing as a "centrifugal force." This is the name commonly given to another physics term known as inertia.

This part is not exactly true. You're right that by "centrifugal force," non-physicists usually mean something else: either inertia, or centripetal force. But there is such a thing as centrifugal force:

Recall that, by Newton's Third Law, for every force there's an equal and opposite force, and that the two constitute an action-reaction pair. Centrifugal force is the force that forms a pair with the centripetal force -- it's the force exerted by the body that's moving in a circle, on whatever's making it turn.

For example, in the case of a yo-yo whirled on a string, the force of the string on the yoyo is centripetal, and the force of the yo-yo on the strong, and thus your finger, is centrifugal. In the case of the car driving in a circle, the ground exerts a centripetal foce on the tires, while the tires exert a centrifugal force on the ground.

You might guess from these examples that it's centripetal force that we usually worry about, not centrifugal. You'd be right. Centrifigal force tends to be a little odd, and mostly irrelevant. I've never seen it matter on an MCAT problem.

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[xanthines]

Sorry, I meant to say something like the Centripetal force isn't really a new type of force, but just the name used to indicate the force pointing inwards. In this case, it is the static frction force.

Since the static coefficient of friction is normally given as the maximum, you know that any more force applied to that object will overcome friction and will begin to slide or in the case of the car, skid off the road.

The centripetal force equation Fc=(m)(v^2)/r describes the force required to keep the object in a circular path. When the car moves fast enough, the force due to static friction will not be high enough to maintain circular motion. Incidentally, I've heard the term "centripetal force requirement" to describe the situation.

Likewise when a satellite or any other thing moves fast enough it will escape the earth's gravity:

G(Mearth)(Msatellite)/(r^2) is less than (msatellite)(v^2)/r

Again, I apologize for the incompleteness of my answer. Hope that helps!

-X

thanks for the quick reply. so when what force is greater than the inward static frictional force does the car start skidding away?

 

[xanthines]

Shrike is right. I meant to say "There is no such thing as centrifugal force acting on you in the car...."

That is still inertia "pushing" you up against the side of the car. Centrifugal force is indeed the force the car exerts on the road.

Mea culpa.

-X