system
Given the following post, respond as if you're commenting on Reddit:
human
Why exactly is a 100% efficient process impossible?

So I've built a perpetual motion device and need your help...

No, actually I'm a BSc Physics grad working on a book and trying to sort some things out in my head. I've been doing a bunch of reading on the topic and am trying to pin down one particular point. I get the basics of the four laws of thermodynamics, I remember the statistical explanations of entropy, and (actually, mostly thanks to a few reddit posts), I'm starting to get a hold of the idea of heat being "unusable" energy.

Ok, so my actual question is this: How valid is it to say that you cannot reach 100% efficiency because you cannot escape friction, and friction always results in a heat transfer? Am I thinking on too much of a macro level?

Thanks for any help you can give.
gpt
Friction is a good culprit in mechanical systems, but equivalent types of loss occur in other systems (e.g. viscosity leads to drag in fluids; randomization of electron paths leads to ohmic resistance in electrical systems).

I think the concept you're reaching for is this:  it is never, in practice, possible to create a completely ordered system, and slight amounts of disorder in any energy-transducing system will yield loss of ordered energy (mechanical, electrical, chemical) to disordered energy (heat at uniform temperature).   Friction is due to lack of order in the physical shape of sliding solids on the molecular scale, or to viscosity in liquids or gases -- which in turn is due to momentum transfer by disordered molecular motion perpendicular to applied shear.  Electrical resistance is due to disorder in the electron-nucleus interaction in a conductor.  Etc.

The problem is that such statements have to be so general (to encompass all the forms of disorder and of ordered energy) that they just boil down to restatements of the second law of thermodynamics.