Joule etc

[Jim Green <JMGreen@SISNA.COM>]

The shy Leigh says --

> I was going to stay out of this (hah!) but as long as I have my oar
> in, let me stir it a bit more. When Joule was twirling his oar he was
> increasing the entropy of the water. It is true that he was not
> heating the water.

Leigh, he surely _was_ "heating" the water:  It got warmer didn't it?  He
just didn't have a hot plate at hand.  Just a Rutherford "heated" the
cannon barrel and water bath -- to the point where the water boiled!!!

> Change in entropy is not associated with an actual
> process;

Of course it is!  And often DS can be calculated -- eg one could calculate
the DS for the classical piston/cylinder even if the piston is plunged
rapidly.  One could calculate the DS for the Joule experiments and then a
DQ -- if one were to define DQ as you suggest below.  But many members of
this list would not so define it -- they want to think of DQ as due to a
temperature difference between some external thermal reservoir and the system.

It can ALSO be
> ..... associated with *any* hypothetical reversible process
> capable of taking an identical system from the same initial to the
> same final state as the system in question. All such processes will
> yield the same path integrals of dQ/T, and the meaning of dQ is well
> defined for the hypothetical process.

OK, I am quite willing to accept a definition of DQ as you suggest --
indeed if it has any meaning at all it must be something like this -- BUT
this is NOT how it is being envisioned  in general on this list.

Jim

Jim Green
mailto:JMGreen@sisna.com
http://users.sisna.com/jmgreen