Re: macroscopic vs microscopic degrees of freedom

[Joel Rauber <Joel_Rauber@SDSTATE.EDU>]

Bob,
wrote and quibbled:
> Except for the restriction to "two systems in contact", this (in my
> reading) is the traditional identification of dQ. Note that it (also
> traditionally) includes all three modes of heat transfer: conduction,
> convection and radiation).

I meant to be only considering the conduction case; certainly if we allow
readiative transfers to occur then I'd call those dQ as well.

Convective cases:  I've always viewed convection as being excluded when I
stated that we were not to consider cases of matter transfer between the two
systems in "contact". (comments?)

> But as I have hitherto ventured, this "ratio divisionis" is
> not unique.
> Other creative accounting methods (of energy balance) are
> possible and can
> be correct.

I think it is important to stress the word *can* in the above.  Perhaps the
partitioning is not unique (I'm not sure I want to say this, at least not
after a particular mechanism and time-scale have been specified.) But it
surely can't be anything?  Or else we don't need the two terms in the 1st
Law. And I think JM is correct to have started is musings on why dQ is
important and needed. Answer: entropy considerations.  That is, the
distinction between dQ and dW may not matter for the internal energy state
function, but may be of some importance in the entropy state function.

Has anybody thought of bringing in other energy state functions into this
discussion; e.g. Enthalpy or Free Energy.  I'm not enough of an expert to
imagine if this would be helpful here or in the discussion of blocks sliding
on surfaces and the consequent 1st law, 2nd law and mechanical work
implications.

Joel

______________________________________________________________

> Bob
>
> Bob Sciamanda (W3NLV)
> Physics, Edinboro Univ of PA (em)
> trebor@velocity.net
> http://www.velocity.net/~trebor
>
> ----- Original Message -----
> From: Joel Rauber <Joel_Rauber@SDSTATE.EDU>
> To: <PHYS-L@lists.nau.edu>
> Sent: Monday, November 01, 1999 10:16 AM
> Subject: Re: macroscopic vs microscopic degrees of freedom
>
>
> > dQ arises from that part of an energy transfer between two
> systems in
> > contact(not to be viewed as a flow, but rather as an accounting
> terminology)
> > that occurs by virtue of a difference in temperature between the
> systems.
> > The transfer of energy that arises from any other means is
> dW; that is,
> the
> > complement to what is dQ.
> >
> > In the above, I'm assuming no transfer of matter between
> the two systems
> in
> > contact.
> >
> > Joel