Re: [Phys-L] work versus mechanical transfer of energy

[John Denker <jsd@av8n.com>]

Here's another point that might be worth a moment's thought:

Feynman famously defined equilibrium as the situation "When all
the fast things have happened, and the slow things have not."
That is a slightly smart-alecky way of saying it, but the idea
is sound:  You can't talk about equilibrium unless you have a
particular timescale in mind, not too long and not too short.

In the heat-leak apparatus I suggested, there are actually
three timescales.  They bracket two different notions of
equilibrium.
  a) We imagine that each block is a good conductor.  It
   rapidly comes into equilibrium /with itself/.  Any new
   bit of energy and entropy is rapidly equilibrated.
   This is important, because it allows us to express
   the energy of the block as a well-behaved function of
   its entropy, and thereby define "the" entropy of the
   block.   
  b) Over a much longer timescale, the two blocks come
   into equilibrium with each other.
  c) On yet-longer timescales, the two-block system will
   leak energy to or from the surroundings.  We engineer
   things so that this is negligible compared to the
   processes we care about.  On yet longer timescales,
   the metal blocks will evaporate into thin air, but
   we don't care about this either.


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Meanwhile ....on 01/07/2016 11:30 AM, Diego Saravia wrote:

> In that case you do not have entropy generation, but you have it!, so your
> model is inconsistent.
>
> just as happens in the two condersers, one charging the other, if you take
> the resistance to cero, your model colapses, if you dont
> take in care another stuff like electrons acelerations, or wave emissions.

That greatly mischaracterizes the model I suggested.  My model
corresponds to two capacitors connected by very high value
resistor (not by a short circuit).  There is no inconsistency.

For any halfway reasonable value of the resistor, the total
energy dissipated in the C-R-C circuit is independent of the
resistor value ... so you can ignore its inner workings.

This is nicely analogous to why you can ignore the inner
workings of the heat-link filament.  The final energy and
entropy values are not sensitive to the details.  The main
thing you need to know is the dE/dS (i.e. temperature) of
each block.