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Rolling & slipping

by dev70
Tags: rolling, slipping
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dev70
#1
Jan11-13, 02:33 AM
P: 58
hi pf, the more i think i have understood classical rotational mechanics the more it turns out to be clumsy? i am just not able to understand the slipping and rolling of bodies? somewhere friction comes into play and somewhere dont?
"if a body rolls without slipping such that velocity of COM doesnt change then no frictional force acts on the body" how? why would a body roll if there is no friction?

please help me out. i am tired of reading so many books. still not able to solve numerical related to it
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A.T.
#2
Jan11-13, 02:51 AM
P: 4,238
Quote Quote by dev70 View Post
why would a body roll if there is no friction?
It's not about how it started rolling. Once it is rolling at constant speed no friction is necessary.
CWatters
#3
Jan11-13, 06:19 AM
P: 3,268
What AT said.

It actually says that in the quote...

"if a body rolls without slipping such that velocity of COM doesnt change then no frictional force acts on the body"
Consider a train that has solid steel wheels (so negligible rolling resistance).... When it accelerates it applies a force on the track in one direction, when it brakes it applies a force in the opposite direction. When it does neither and travels at a constant velocity no frictional forces are acting.

Aside: In a real train this isn't true because of things like wind resistance and rolling resistance isn't totally zero. So some force (and power from the engine) is required to maintain a constant velocity.

dev70
#4
Jan11-13, 12:36 PM
P: 58
Rolling & slipping

ok..if i consider a sphere rolling as well as sliding down an inclined plane? what should i interpret? friction is acting or not?
Doc Al
#5
Jan11-13, 12:48 PM
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Quote Quote by dev70 View Post
ok..if i consider a sphere rolling as well as sliding down an inclined plane? what should i interpret? friction is acting or not?
If the sphere is rolling without slipping down the incline then there must be a friction force to produce the angular acceleration.


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