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Does a substances friction increase with increased heat?

  1. Jun 8, 2004 #1
    Assuming it stays a solid, if something gets colder, it seems, it's molecules become more tightly compressed and less able to drag on things and vice versa. Is that assumption correct?
     
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  3. Jun 9, 2004 #2

    Gokul43201

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    In general, no. The coefficient of friction is dot defined on a single material, but for a pair of surfaces. It only depends on the surface texture - the bulk properties like density (which is what you are describing) have no effect on the coefficient of friction.
     
  4. Jun 9, 2004 #3
    So then why does NASCAR heat their tires prior to installation during a pitstop. Are you saying hot and cold tires have the same COF when running on the same track?
     
  5. Jun 9, 2004 #4

    Gokul43201

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    No, I'm not. You are right that hot tires have better traction.

    My explanation was for a general solid which does not undergo (inter)molecular rearrangement upon heating. In the case of tires, the heat softens the rubber and as a result increases its coefficient of friction.

    So there are cases where the temperature affects the coefficient of friction (such are in polymeric materials like rubber), but you can not draw up a generic relation between temperature and friction coefficient.

    Most other common solids, don't behave this way, unless you get really hot, at which point there are recrystallization effects that may lead to a change in the CoF through plastic flow/creep.
     
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