Odd Cases of Kinetic Friction vs. Static Friction

[kobe200LATE]

So we all know that static friction refers to the force of friction that must be overcome required to get something to start moving and kinetic friction refers to the friction when an object is already in motion, but there are also weird cases where you would use static friction instead of kinetic or kinetic instead of static.

One example would be a rolling wheel. You would think that it would use kinetic friction because its moving, but you are actually supposed to use static friction.

Does anyone else know any weird cases like this with static vs. kinetic friction?

Thanks,
KOBE-2 THOUSAND-AND-LATE

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[BerkReviewTeach]

So we all know that static friction refers to the force of friction that must be overcome required to get something to start moving and kinetic friction refers to the friction when an object is already in motion, but there are also weird cases where you would use static friction instead of kinetic or kinetic instead of static.

One example would be a rolling wheel. You would think that it would use kinetic friction because its moving, but you are actually supposed to use static friction.

Does anyone else know any weird cases like this with static vs. kinetic friction?

Thanks,
KOBE-2 THOUSAND-AND-LATE

Replace the word "moving" with the word "sliding", and it might clear all those examples up. A rolling wheel is not sliding, so it cannot be kinetic friction. A person walking is not sliding (unless they are in socks on a waxed floor), so that cannot be kinetic friction either.

Just figure that anything that does not involved sliding surfaces cannot be kinetic friction, and therefore must be static friction.

 

[kobe200LATE]

ok so in a nutshell things that slide involve kinetic friction and things that don't slide involve static friction?

 

[sv3]

Replace the word "moving" with the word "sliding", and it might clear all those examples up. A rolling wheel is not sliding, so it cannot be kinetic friction. A person walking is not sliding (unless they are in socks on a waxed floor), so that cannot be kinetic friction either.

Just figure that anything that does not involved sliding surfaces cannot be kinetic friction, and therefore must be static friction.

I'm going to have to dedicate a full mcat point to you my friend........(doesn't sound like alot but some days I am sure it will be about 50% of my total)