Can kinetic friction be greater than static friction? How can this be tested?

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Discussion Overview

The discussion centers around the question of whether kinetic friction can be greater than static friction, exploring the conditions under which this might occur and how such a scenario could be tested. Participants express varying opinions on the nature of friction, its measurement, and the underlying physics involved.

Discussion Character

  • Debate/contested
  • Exploratory
  • Conceptual clarification

Main Points Raised

  • One participant mentions that their physics teacher suggested that under certain conditions, kinetic friction could exceed static friction, but the specifics of such a setup are unclear.
  • Another participant expresses skepticism, stating that the understanding of friction is incomplete and doubts the possibility of kinetic friction being greater than static friction.
  • A different viewpoint suggests that static friction can be equal to kinetic friction but not greater, while a subsequent post corrects a mistyped statement to assert that kinetic friction cannot be greater than static friction.
  • One participant proposes a scenario involving varying normal forces that could lead to uneven levels of static and kinetic frictional forces.
  • Another participant speculates that the material properties of an object could change due to heat generated by friction, potentially affecting the coefficient of friction and leading to a situation where the object stops moving despite a constant applied force.
  • A later reply argues against the possibility of kinetic friction being greater than static friction, presenting a reasoning based on the mechanics of force application and movement, citing a contradiction in such a scenario.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether kinetic friction can be greater than static friction. Multiple competing views are presented, with some participants firmly opposing the idea while others suggest potential conditions that could allow for it.

Contextual Notes

Some statements reflect uncertainty about the underlying principles of friction, and there are references to varying conditions that could influence frictional forces, but these remain unresolved within the discussion.

SelmerSaxMan
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Hi all. My physics teacher told me a while ago, that, under certain conditions a situation could be made in which kinetic friction is greater than static friction. He didn't know how this was done. Would anyone here be able to tell me how one would set this situation up and how he would measure the results?
 
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By the way, this isn't homework related, this is for my own interests, if that is which makes a difference in inspiring a reply to the question begged.
 
Since our understanding of friction is still very incomplete its hard for me to say why... but I don't think that's possible. I'm interested to see what someone else might chime in with.
 
i think static friction can be equal to kinetic friction but not equal.
 
sorry
kinetic friction can be equal to static friction but not greater than static friction.

please forgive me, mistyping.

-benzun
 
we know that the proventive force of a abject in motion due to friction is a function of the normal force. What if you have a situcation where is there is a varying( uneven) level of such normal force? This wil will cause an varying( uneven) level of static v.s kinetic frictional forces? Can this work?
 
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hmmm interesting question. I would say it would have something to do with a special material for the object that's moving, such that, as the object moves and the contact surface heats up due to friction, the surface undergoes some physical or chemical change so that its coefficient of friction increases.

This would mean if you started to push the object on a flat plane so that it just starts moving (and then keep pushing with that same constant force), then as the heat builds up and the critical temperature is reached that the object halts to a stop even though you are still applying the same constant force...

(kant is also correct in a way, for example if you increase the mass of the object that is moving (say a bucket of sand that you continally add sand to)).
 
It's impossible.

Imagine if kinetic friction is greater than static friction. If you pull (or push) a box of a certain weight on a flat floor, gradually increasing pulling force. When the force becomes greater than the static friction force, the box will begin to move, but at that point due to greater kinetic friction, this box must not be moving. This is a contradiction and the reason static friction must be always greater than or equal to kinetic friction.

Hope this helps.

I've read this discussion in a Feynman's book (Feynman's lectures on physics). I think it's in vol. 1. But alas, it's not at hand now.
 
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