# How is it possible that friction = centripetal force for turns?

by x86
Tags: centripetal, force, friction, turns
P: 3,918
 Quote by Frosted Flake A magnet stuck to a fridge is not at rest. It's just stuck. A car parked on an incline is not at rest. It's just parked.
You seem to have a strange concept of "rest".
P: 14
 Quote by A.T. You seem to have a strange concept of "rest".
Not at all.

A car on a hill will roll down the hill. It is the brake, acting continuously, that prevents the car from rolling.

A magnet stuck to a fridge would, if not for the magnetic force, fall to the floor.

In both cases friction, STATIC friction... acts continuously to prevent motion that would otherwise occur. An object held in place by a force is stationary. But being at rest means it stays where it is without applying a force to keep it there.
 P: 828 That is not an accurate definition of "at rest". I don't know who told you that, but it's incorrect. An object at rest will remain at rest unless acted upon by an unbalanced force. Saying that an object needs to be completely devoid of forces to be at rest is ridiculous.
P: 3,918
 Quote by Travis_King Saying that an object needs to be completely devoid of forces to be at rest is ridiculous.
Yeah, now I can't even have a rest on my bed.
 P: 14 Travis. A.T. Please pick up a bowling ball. Hold it at arms length, head high. Now, rest. Does it not upon due examination turn out that YOU, yes YOU, were holding the ball up? And what happened to the ball? Did it not achieve of it's own volition the lowest potential energy state available to it? And what exactly is your quibble?
 P: 262 Frosted, your semantics are irrelevant. The physical concept of an object being at rest is simply that it does not move. It may be used in slightly different ways outside of physics, but within physics, this is not negotiable - it is simply the way it is used.
 P: 14 Well then. You better forget everything I said.

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