Does a substances friction increase with increased heat?

In summary, the coefficient of friction between two surfaces is not affected by the temperature of the material, but rather by the surface texture. However, in the case of polymeric materials such as tires, heating the material can soften it and increase its coefficient of friction. This is not a general relationship, as other common solids do not behave this way unless they are at very high temperatures.
  • #1
wasteofo2
478
2
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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  • #2
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.
 
  • #3
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?
 
  • #4
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.
 

1. Does the type of substance affect its friction with increased heat?

No, the type of substance does not have a significant effect on its friction with increased heat. Friction is a property of the surface of an object and is affected by factors such as roughness, temperature, and pressure, but the type of substance itself does not have a direct impact on friction.

2. How does increased heat affect the roughness of a surface and its friction?

Increased heat can cause a surface to expand, which may increase its roughness and therefore its friction. This is because the molecules in a heated substance move more rapidly, causing the surface to become more irregular and creating more points of contact with another surface, resulting in increased friction.

3. Is there a limit to how much a substance's friction can increase with increased heat?

Yes, there is a limit to how much a substance's friction can increase with increased heat. This is because at extremely high temperatures, the molecules in a substance may begin to break apart or melt, which can decrease the amount of friction between surfaces.

4. Does the direction of heat flow affect a substance's friction?

Yes, the direction of heat flow can affect a substance's friction. When heat is applied to a substance, it can cause the molecules to move in a particular direction, which can influence the direction of friction forces between surfaces.

5. Can increased heat cause a substance's friction to decrease?

Yes, increased heat can cause a substance's friction to decrease in certain cases. For example, if a substance melts or vaporizes at higher temperatures, it may lose its ability to create friction with another surface. Additionally, at extremely high temperatures, the molecules in a substance may break apart, resulting in a decrease in friction.

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