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Angular momentum question

  • Thread starter radagast_
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  • #26
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It needs friction to start rolling, or to accelerate the vehicle, or to stop rolling.

But it doesn't need friction to roll at a constant rate.

If there is no friction, the wheel's forward velocity will stay the same, and its angular velocity will stay the same.

Consider a log on (frictionless) ice - if you manage to start it rolling without slipping, it will carry on doing so for ever.
a log is different from a wheel!!!!!!!!!!!!!!!!

Why do cars skid on rainy days? Because there is lower friction with the road. Thus when they turn, the torque is too much for the wheels to handle thats why they slip
 
  • #27
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My take is that friction always assists rolling.

As far as slipping is concerned , slipping does not necessarily imitate rolling. it is rolling along with a component of frictional force acting along and back the wheel.

rolling objects to frictional force at any point of contact.
 
  • #28
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a log is different from a wheel!!!!!!!!!!!!!!!!

Why do cars skid on rainy days? Because there is lower friction with the road. Thus when they turn, the torque is too much for the wheels to handle thats why they slip
I object.

It is not the torque that causes it to skid. The centripetal force is minimised and thus the tangential component of velocity takes advantage and the car skids.

Friction always necessarily keeps the body in circular motion.
 
  • #29
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if we were to apply a foce to a wheel on a frictionless surface, the wheel will simply accelerate without turning.

If a wheel is rolling and friction is taken out, then the wheel would contrinue rolling.

when a wheel slips, it means that the torque is too much for the friction to handle.
 
  • #30
tiny-tim
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if we were to apply a foce to a wheel on a frictionless surface, the wheel will simply accelerate without turning.
(I take it you mean a stationary wheel)

It depends where you apply the force.

If the point of application is the centre of the wheel (or if the line of application passes through the centre), then I agree. But if the point of application is off-centre, then the wheel will accelerate and will start to turn.

You agree?

Then, if you judge the point of application right, the velocity and the turn may match, and there will be no slipping - even on ice! :smile:
 
  • #31
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(I take it you mean a stationary wheel)

It depends where you apply the force.

If the point of application is the centre of the wheel (or if the line of application passes through the centre), then I agree. But if the point of application is off-centre, then the wheel will accelerate and will start to turn.

:
yes that was what i meant. The difference being that if there was friction, then the wheel would turn.

again, i thought that slipping means that something doesn't have enough grip. And with grip you have friction. So in order to see when the wheel would slip, you gotta have friction for that./
 
  • #32
tiny-tim
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yes that was what i meant. The difference being that if there was friction, then the wheel would turn.
You're missing my point, that even that if there is no friction, then the wheel can still turn:
But if the point of application is off-centre, then the wheel will accelerate and will start to turn.

You agree?

Then, if you judge the point of application right, the velocity and the turn may match, and there will be no slipping - even on ice! :smile:
Do you agree? :smile:
 

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