Friction is electricmagnetic force; why friction is not conserved?

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Discussion Overview

The discussion revolves around the nature of friction as a force, specifically questioning why friction is not considered a conserved force, despite being linked to electromagnetic interactions. Participants explore the definitions of conservative forces and the implications of energy conservation in the context of friction.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant asserts that friction is not a result of the other three fundamental forces and questions its conservation.
  • Another participant states that energy is always conserved, arguing that for a force to be conservative, it must satisfy the condition of a closed loop integral being zero, which friction does not meet.
  • A different viewpoint suggests that while many macroscopic forces, including friction, arise from electromagnetic interactions, the increase in kinetic energy at the microscopic level does not translate to an increase in the kinetic energy of macroscopic bodies, indicating that mechanical energy is not conserved.
  • A participant provides an analogy involving the sensation of friction when pushing or pulling objects, questioning the nature of the force experienced in different scenarios.
  • One participant seeks clarification on whether the original question pertains to friction being a non-conservative force, noting that while the electromagnetic force is generally not conservative, the electrostatic force is an exception.

Areas of Agreement / Disagreement

Participants express differing views on the nature of friction and its classification as a conservative force. There is no consensus on the relationship between friction and electromagnetic forces or on the implications of energy conservation in this context.

Contextual Notes

Participants reference the definitions of conservative forces and the conditions under which energy is conserved, but the discussion does not resolve the complexities surrounding the definitions and implications of these concepts.

Haorong Wu
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Obviously, friction is not a result of other three kinds of force, and electricmagnetic force is conserved, then why friction is not conserved?
 
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Energy is always conserved, so that is not relevant. For a force to be conservative it must satisfy ##\oint \vec F \cdot d\vec r = 0## which friction does not.
 
Forces may be conservative (or not). There is no such thing as "conservation of forces".

If you look at a microscopical picture, indeed most of the macroscopic forces (not just friction) are the result of electromagnetic interactions. But then you have to be consistent with the microscopic view. The result of friction is the increase in the kinetic energy of some molecules but this increase does not result in an increase of the KE of the macroscopic bodies.
So as Dale said, the energy is conserved.
The mechanical, macroscopic energy is not.
 
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If you are sitting at the breakfast table and gently push your bowl away from you, you can "feel" the friction, right -- you have to "push"? Now when you pull the bowl back closer to you do you feel the same, or does the bowl seem to be pushing your hands along?

Now compare that to say, picking up a suitcase. You pull on up the handle, the suitcase rises up from the floor. When you let it back down, you feel it pulling down? Or do you have to push it back down?
 
Haorong Wu said:
Friction is electricmagnetic force; why friction is not conserved?
Did you mean to say "why friction is not a conservative force"?

The electromagnetic force in general is also not conservative.

The electrostatic force (Coulomb's law) is indeed conservative, and you can define a potential energy for it. However, the "electrodynamic" force (e.g. in Faraday's law) is not conservative, neither is the magnetic force in general.
 
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