Does a substances friction increase with increased heat?

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Discussion Overview

The discussion centers on the relationship between a substance's temperature and its frictional properties, specifically whether increased heat affects friction. Participants explore this concept in the context of solid materials, with a focus on both general principles and specific applications, such as tire performance in racing.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that as a substance cools, its molecules become more tightly compressed, potentially affecting friction.
  • Another participant counters that the coefficient of friction is defined for pairs of surfaces and primarily depends on surface texture, not on bulk properties like density.
  • A follow-up question challenges the idea by asking why NASCAR heats their tires if hot and cold tires have the same coefficient of friction when on the same track.
  • A participant clarifies that while general solids may not show a relationship between temperature and friction, in the case of tires, heating softens the rubber, increasing its coefficient of friction.
  • It is noted that temperature can affect the coefficient of friction in specific materials, such as polymers, but a generic relationship cannot be established for all solids.
  • There is mention of potential changes in the coefficient of friction at high temperatures due to recrystallization effects and plastic flow/creep.

Areas of Agreement / Disagreement

Participants express differing views on the influence of temperature on friction, with some acknowledging that it can vary based on material type, while others maintain that a general rule cannot be applied across all solids. The discussion remains unresolved regarding the extent and conditions under which temperature affects friction.

Contextual Notes

Limitations include the dependence on material types and conditions, as well as the need for further clarification on how temperature interacts with friction in various substances.

Who May Find This Useful

This discussion may be of interest to those studying material science, engineering, or physics, particularly in relation to friction and thermal effects on materials.

wasteofo2
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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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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.
 
Gokul43201 said:
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.

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?
 
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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