Direction of Friction for Rolling Spheres on Rough Surfaces

[SDewan]

Hi all,
Can anyone please help me out with the direction of friction in a case where there is a smooth spherical body pure rolling on a rough surface? What is the direction of friction?
Also, is it possible to have pure rolling without friction?

Thanks
SD

 

[gracy]

is it possible to have pure rolling without friction?

Go through the following

https://www.physicsforums.com/threads/paradox-pure-rolling-and-friction.676354/

 

[BvU]

Depends on the inital situation. Most frequent case: if a ball is sliding over a surface, the backwards friction will make it change over to rolling without slipping.

But if it hits the ground spinning like crazy (around a horizontal axis), the forward acting friction will accelerate the motion while adjusting the rate of rotation until there is no more slipping.

And yes: pure rolling without friction is possible. All that is required is $v = \omega R$ (speed = angular speed times radius)[edit] sorry, missed the 'pure' as in pure rolling (meaning rolling without slipping). Agree with Russ #5.

 

[sophiecentaur]

Also, is it possible to have pure rolling without friction?

You can always potential run into trouble if you work with models that are a mixture of ideal and practical. If you have 'no friction' then your model is very limited. You have to work with a very low value of friction - not zero.

And yes: pure rolling without friction is possible. All that is required is v=ωRv=ωRv = \omega R (speed = angular speed times radius)

You would need to set up that condition with some external force to produce the rolling.

 

[russ_watters]

You can always potential run into trouble if you work with models that are a mixture of ideal and practical. If you have 'no friction' then your model is very limited. You have to work with a very low value of friction - not zero.

You would need to set up that condition with some external force to produce the rolling.

I think life is simpler: any time an object is rolling without slipping at constant speed, the friction force is zero - regardless of how it got to be that way.

If you want to quibble about exactness of such a scenario, roll a ball down a shallow incline. At some point it will reach a terminal velocity, where friction against the surface is exactly zero.

 

[sophiecentaur]

I think life is simpler: any time an object is rolling without slipping at constant speed, the friction force is zero - regardless of how it got to be that way.

If you want to quibble about exactness of such a scenario, roll a ball down a shallow incline. At some point it will reach a terminal velocity, where friction against the surface is exactly zero.

You're right . . . . . until you have to deal with yet another question on PF about it.

 

[A.T.]

Can anyone please help me out with the direction of friction in a case where there is a smooth spherical body pure rolling on a rough surface? What is the direction of friction?

https://www.physicsforums.com/threads/investigation-of-a-rotating-cylinder.770027/#post-4847396