Things giving rise to static and dynamic coefficients of friction?

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Discussion Overview

The discussion revolves around the factors influencing static and dynamic coefficients of friction, exploring various physical concepts and phenomena related to friction, energy transfer, and deformation. Participants delve into both theoretical and practical aspects, including the nature of surfaces, energy dissipation, and the implications of different types of deformation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that topography, mass, moisture, atmospheric pressure, and magnetism contribute to the coefficients of friction.
  • Others mention dust and asperities as significant factors affecting friction.
  • A participant questions the existence of perfectly smooth surfaces outside of mathematical abstraction, suggesting spacetime as a potential example.
  • There is a recurring inquiry about the energy dissipation during frictional interactions, with some suggesting it primarily converts to heat.
  • One participant distinguishes between static and sliding friction, noting that energy is stored as elastic deformation in static friction, while sliding friction involves bond breaking and heat generation.
  • Another participant emphasizes that energy is required for deformation but argues that it need not be kinetic energy, introducing the idea of deformation occurring at low speeds requiring minimal kinetic energy.
  • Hysteresis is introduced as a concept related to energy loss in materials, with a participant seeking clarification on its implications in friction.
  • There is a discussion about the relationship between energy, stress, and temperature, with varying opinions on how these concepts interact.
  • Some participants explore the implications of equilibrium on heat transfer and energy flow, referencing the second law of thermodynamics.
  • A later reply introduces the concept of negative temperatures, prompting further curiosity among participants.

Areas of Agreement / Disagreement

Participants express a range of views on the factors affecting friction and energy transfer, with no clear consensus reached. Disagreements arise regarding the nature of energy required for deformation and the relationship between stress and temperature.

Contextual Notes

Some discussions involve complex interactions between energy, heat, and material properties, with participants acknowledging the need for further clarification on concepts like hysteresis and equilibrium. The conversation also touches on theoretical aspects that may not have straightforward applications.

Who May Find This Useful

This discussion may be of interest to those studying physics, materials science, or engineering, particularly in relation to friction, energy transfer, and material behavior under stress.

  • #31
If you really want to dive into this subject, you should study the fluctuation dissipation theorem. This should take a few weeks or longer.
 
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  • #32
Frabjous said:
No, relative velocity between the surfaces. There are plenty of measurements of different friction coefficients at different velocities for a variety of systems.
Don't those depend on the masses of the surfaces though, and therefore momentum? Or is it simply velocities and topography?
 
  • #33
I am not a friction expert. Most general theories take adhesion and plastic deformation into account. (To account for different materials having different properties, one could look at suface/interfacial energies.) So anything that effects these things matters.

Look at a frictional system of two different materials. I can choose either system to be at rest. How does one define “momentum” in this case?
 
  • #34
Frabjous said:
I am not a friction expert. Most general theories take adhesion and plastic deformation into account. (To account for different materials having different properties, one could look at suface/interfacial energies.) So anything that effects these things matters.

Look at a frictional system of two different materials. I can choose either system to be at rest. How does one define “momentum” in this case?
In the case of dynamic friction, you'd look for which one is doing the disturbing of the topography of the other one. That one would have more momentum, or non-zero momentum.
 
  • #35
jaketodd said:
In the case of dynamic friction, you'd look for which one is doing the disturbing of the topography of the other one. That one would have more momentum, or non-zero momentum.
I can measure the force of friction in either frame and it is identical. Saying that there is a preferential frame that depends on microstructural behavior is extremely cumbersome. What if I heated the ”hard” plate so that it became the ”soft” plate?

We general(edit: +ly) like physics to be frame independent.
 
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  • #36
Frabjous said:
We general like physics to be frame independent.
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https://www.thegeneral.com/about/contact/
 
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  • #38
Yum!
 
  • #39
How do you guys know I have an emergency stockpile of SPAM??

Yes, Sizzle some Pork And Mmmm.
 
  • #40
Frabjous said:
What if I heated the ”hard” plate so that it became the ”soft” plate?
Then they would both be frictionless surfaces to one another and there would be no coefficients of friction between them.
 
  • #41
jaketodd said:
Then they would both be frictionless surfaces to one another and there would be no coefficients of friction between them.
No, there would still be friction between them.
 
  • #42
Frabjous said:
No, there would still be friction between them.
I'm sorry; I thought you meant that the plates would be separate.

But in discrete space and discrete bodies, there will always be friction, because there is a smallest unit, always a "roughness." But if possible, continuous for both, I suppose total frictionless is possible, at least in theory.
 
  • #43
jaketodd said:
I'm sorry; I thought you meant that the plates would be separate.

But in discrete space and discrete bodies, there will always be friction, because there is a smallest unit, always a "roughness." But if possible, continuous for both, I suppose total frictionless is possible, at least in theory.
There are also adhesive forces so probably not.
 
  • #44
Frabjous said:
There are also adhesive forces so probably not.
I suppose in discrete space, smallest units, it's possible for there to be perfect smoothness, but not if near a gravitating body, because then all the quanta would not match up perfectly. Warped discrete spacetime.

Adhesive forces, good point, like gravity of the two surfaces, however weak. Unless there's a smallest unit of gravity, and the two surfaces are not at the threshold to have any gravity. But then there's all the other factors mentioned in this thread that can increase the friction coefficients.
 
  • #45
jaketodd said:
Adhesive forces, good point, like gravity of the two surfaces, however weak
Or chemical bonding.
 
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