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As we know, when an object slides over a "bumpy" surface, hitting the bumps and causing them to deform, it generates heat and some of the kinetic energy of the object is lost as its velocity decreases, as elegantly depicted in this animation. Furthermore, we know that heat is generated from the collisions between the atoms on the object and the surface atoms. A post on this site describes how these collisions cause shock waves, i.e. traveling vibrational motion in the atoms adjacent to the collision.

My question is whether besides the heat generated from the shockwave, whether heat is also absorbed from bonds that formerly held the bumps to the rest of the surface material being broken.

If energy is indeed released from these bonds, we would see higher coefficients of friction in materials held together with stronger bonds, and more energy is absorbed when stronger bonds are broken in hypothetical materials with identical microstructural geometries and different compositions. Is this one of the factors that determines coefficients of friction? Has anyone been able to isolate the heat-absorbing effects of the atoms colliding from the heat-absorbing effects of bonds being broken?

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    $\begingroup$ energy being stored in the broken intermolecular bonds” It’s a misconception that bonds store energy. Bonds release energy when they form and require energy to break. I’m not sure how this affects your hypothesis? $\endgroup$ Jun 2, 2022 at 23:45
  • $\begingroup$ Thank you for your correction. I've updated my question to say instead that potential energy in the bonds is released, instead of "energy being stored". Given that heat is still released from bonds being broken, I don't think that it affects the essence of my question. $\endgroup$ Jun 3, 2022 at 14:51
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    $\begingroup$ Given that heat is still released from bonds being broken…” Again, energy is absorbed, not released, when bonds are broken. $\endgroup$ Jun 3, 2022 at 16:27
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    $\begingroup$ I believe what @Chemomechanics is saying is that bonds are a force. The breaking of surface atom bond is simply an impulse that will create a change in the kinetic energy of both the released atom and the remaining material. Heat is not being released. Some of the kinetic energy is passed on to the bulk material as vibrational energy that can be measured as a change in temperature. $\endgroup$ Jun 3, 2022 at 17:13
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    $\begingroup$ I don’t understand what’s being compared. Stronger bonds are also less likely to break, so I don’t see how the heat absorbed can be independently varied. $\endgroup$ Jun 4, 2022 at 17:07

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Friction results from the transition of an ordered macroscopic movement into unordered microscopic movement. This transition is caused by the high dimensionality of the corresponding (quantum)dynamic problem together with the conjecture that an overwhelming fraction of the phase space volume evolves into states arbitrarily close to any other chosen state (ergodic hypothesis). Whatever is determining the dynamic problem is part of the effect of friction, among of which are scattering processes/collisions as well as bound states opening and closing.

Just try it with some glue under your shoes.

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The coefficient of friction is a unitless ratio of the force opposing the direction of motion (friction) to the normal force. Any phenomena that changes the frictional force will change the coefficient of friction. Since friction is mostly surface dependent, any surface molecular forces due to adhesion, dangling surface bonds, surface roughness, intermolecular or intramolecular forces will contribute to the overall force. Now, the question you are really asking is:

Does surface temperature also affect the coefficient of friction?

The answer is yes but it's complicated since all the contributing forces are temperature dependent and material dependent. See:

Does coefficient of friction depend on temperature?

https://aapt.scitation.org/doi/10.1119/1.1869429

https://www.cycleworld.com/story/blogs/ask-kevin/friction-varies-with-temperature/

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