# Is the relation between change in potential energy and work by internal conservative force can be used even in presence of non conservative forces?

We know that work done by internal conservative forces is the negative of change in potential energy of the system stored in conservative force field. But does this logic still hold when there are non-conservative forces like friction or resistance?

Do the non-conservative forces only withdraw from the kinetic energy part and not affect the potential energy in any way? Consider for an example a system of two charges having some mass kept at a finite distance and both are free to move over a rough surface and released.

Non-conservative forces change the total mechanical energy of the system, since $$W_\text{nc}=\Delta E=\Delta K+\Delta U$$ assuming all conservative forces are internal to the system.