Re: dW turns into dQ

[Joel Rauber <Joel_Rauber@SDSTATE.EDU>]

J Denker wrote in part:

> > Instead of trying to decide if some activity was dW or not,
> lets decide if
> > it is dQ or not.
>
> A fine idea.  Let's see where it leads.
>
> > dQ arises from that part of an energy transfer between two systems in
> > contact
>
> [pause]
>
> > (not to be viewed as a flow, but rather as an accounting terminology)
>
> I don't mind calling it a flow.  But an accounting is OK too.

Actually I don't mind calling it a flow either, but there are those that do,
and that is not the point of contention in this discussion.

> > that occurs by virtue of a difference in temperature between
> the systems.
>
> Whoa!  I cannot endorse such a narrow restriction on the
> meaning of dQ.
> There exist of course certain restricted problems for which
> that is the
> only form of dQ that need be considered -- but that is
> certainly not the
> general case.

I suspect that you mean more than Bob's comment regarding radiative
transfers.  If not then we agree to this point.

> > The transfer of energy that arises from any other means is
> dW; that is,
> the
> > complement to what is dQ.
>
> Depending on how much one reads into that statement, it might
> lead to a
> subtle misconception, namely that every energy-transfer process has a
> definite way of partitioning the energy between dQ and dW.

I think that I am argueing that a specifice process, hence a specific
time-scale, does come close to having a definite way of partitioning
between dQ and dW.  (see Leigh's comments on classical thermodynamics and
entropy).  I'm thinking off-the-cuff here; for discussion purposes.

If the partitioning is totally arbitrary once a specific process and
time-scale is determined, why bother partitioning at all?

> There's an entire concept that seems to have been
> short-changed in this
> discussion, namely the idea of a dissipative process that
> creates new heat
> where there was none before.

Here I think we part company, and the Joule paddle wheel experiment suffices
here.  It is a dissipative process.

To my mind, the Joule mechanical equivalent of heat paddle wheel experiment
is describing a process where the transfer is dW.  And Joule points out (by
experimental proof) that this process is equivalent to some other process
where the the transfer is all dQ.  (put the apparatus on the burner without
turning the crank, and achieve the same temperature rise).  The two
different processes that occurred had a definite partitioning.

To be sure, I can't simply look at the initial state and the final state and
know the partitioning.  I have to know the process as well.  (I assume
knowing the process means knowing the time-scale as well.)

JM & JD (any comments?)

Joel