Friction on pure rolling non deforming sphere?

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Discussion Overview

The discussion revolves around the mechanics of friction acting on a sphere that is purely rolling on a horizontal, non-deforming surface. Participants explore the implications of pure rolling motion, the nature of contact points, and the role of friction in this idealized scenario.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions how friction operates on a sphere that is purely rolling, noting that there is only one point of contact at any time and suggesting that this may affect the application of friction.
  • Another participant posits that if both the sphere and surface are non-deforming, rolling resistance would be absent, leaving only air resistance to slow the sphere down.
  • A different viewpoint emphasizes that while the velocity of the contact point is zero in pure rolling, the pressure at the contact point could theoretically be infinite due to finite contact force, raising questions about the nature of friction in this context.
  • One participant reiterates the concept of the contact point's velocity being zero and challenges the framing of the question, suggesting a misunderstanding regarding frictionless interactions.

Areas of Agreement / Disagreement

Participants express differing views on the nature of friction in this scenario, with no consensus reached on how friction operates under the conditions described. The discussion remains unresolved regarding the implications of pure rolling on frictional forces.

Contextual Notes

There are assumptions regarding the idealized nature of the sphere and surface, and the discussion does not address potential real-world factors such as material properties or external forces that could influence the behavior of the system.

tbn032
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How will the friction work on a sphere which is purely rolling on a horizontal surface such that both the sphere and surface does not deform. The sphere at any time t will only have one point of contact, which would continuously changing as the sphere rolls. Will The friction be applied to the sphere and will it stop rolling?. Since there is one point of which pass vertically through the center of mass, there would not be any counter torque due to normal forces. The velocity of contact point would be zero since it is pure rolling.
 
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If the sphere and surface are not deforming, there is no rolling resistance, right? So you are only left with some air resistance opposing the sphere's linear movement, which will eventually slow the sphere to a stop.
 
tbn032 said:
The velocity of contact point would be zero since it is pure rolling.
True, but for a finite contact force, the pressure at the point of contact would be infinite, and so beyond the strength of any real material. Friction is independent of the area of contact or pressure. Friction is proportional only to the total contact force.

It is the locus of the contact point that moves as the object rolls, not the contact point. In your ideal geometric model, each contact point exists for only one instant. Without time, the contact point cannot have a velocity, but the locus of all the instant contact points does have a velocity.
 
tbn032 said:
How will the friction work on a sphere which is purely rolling on a horizontal surface such that both the sphere and surface does not deform. The sphere at any time t will only have one point of contact, which would continuously changing as the sphere rolls. Will The friction be applied to the sphere and will it stop rolling?. Since there is one point of which pass vertically through the center of mass, there would not be any counter torque due to normal forces. The velocity of contact point would be zero since it is pure rolling.
You mean "how does friction work between a frictionless object and a frictionless surface?"
 
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