Question

Does the conservation of energy still holds for non conservative-force ?And how do we find the potential energy of a non-conservative force ? Should we describe the path ?

Answer 1

Of course it doesn't hold 'cause the object having some energy looses it in the form of for e.g. heat.
In the conservative fields, where conservative forces act on the objects, the objects don't loose energy, but forces change its form. No energy is transmitted to other objects( that was the case in non-conservative fields, heat was transmitted to universe), so total energy remains the same.

Answer 2

Sorry but shouldn't the conservation of energy be universal ? How can it be violated?

Answer 3

There is Total energy (including thermal energy) and there Mechanical energy (excluding microscopic forms of energy).
When we say "conservation of energy", it depends which type you are taking about. When we speak of a conservative system, we mean its Mechanical energy is conserved.

In the case of a non conservative force, there is no potential energy. The two exclude each other.

Answer 4

Ok, so the Work-Energy theorem states that there is a conservation of energy in a conservative system, but if there is a system on which are acting non conservagive force... then for this system the conservation of energy doesn't hold... right ?

Answer 5

Change in mechanical energy = sum of works by all (external AND internal) non-conservative forces.

Answer 6

Energy, broadly defined, is always conserved. In some cases it becomes heat through friction, in other cases, rest mass is converted to energy, E = mc^2.