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My understanding about conservative force is a force that its work is independent of path such that we can construct another form of the work called potential to make our life easier.

For friction, if I start from microscopic point of view, it should be the macroscopic effect of the electric force or gravity which are both conservative force.

Why do we initially have description by conservative forces (electric/gravity force) but end up with a macroscopic description of nonconservative force(friction)?

Qmechanic
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Yi-Ping Huang
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2 Answers2

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Coming at the problem from a philosophical level (rather than a detailed look at the micro-physics), I like to note that the"non-conservative" forces you encounter in day-to-day life don't break the conservation of energy in general: then only break the conservation of a-few-specified-types-of-energy-that-we've-studied-in-class-so-far.

That is to say that the energy "lost" during a physics 101 laboratory on friction ends up as heat (and sometimes sound) which we generally haven't addressed at that point in the course.

The origin of this kind of non-conservativeness is physics happening on a scale (in distance or time) that we are ignoring. To a large degree this comes down to thermodynamics and in particular that pesky second law.

dmckee --- ex-moderator kitten
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Not all forces on the microscopic scale add up to a force on the macroscopic scale. Some create motion on a microscopic scale, which we see as temperature on a macroscopic scale. So thermal energy is "lost" and the force is nonconservative.

Stein
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