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Re: Thermodynamics essay



At 01:55 PM 10/10/01 -0500, RAUBER, JOEL wrote:
My quibble is that JD states that the structure of the usual form of the
first law can not handle all five cases. I hope to show that it can handle
all five cases by explicit construction. (usual structure = Delta E = W +Q
)

For the sake of definiteness, lets stipulate 10 units of energy is
transfered from A to B.
...
3)Energy could leave A in thermal form and arrive at B in nonthermal form.

Delta E = 10
Q = 10
W = 0
...
By explicit construction the structure of the usual statement has
accomodated all five cases.

I'm not buying the analysis of case 3 in particular.

I hope its clear that the following is at least consistent.

"Energy could leave A in nonthermal form" --> that is W
"Energy could leave A in thermal form" --> that is Q

Well, it's clear enough. It is self-consistent in the narrowest possible
sense, from A's point of view. But it is unphysical and unconventional,
and it is inconsistent with any attempt to understand things from B's point
of view.

> It is bad practice to have Q mean one thing on Monday and
> another thing on
> Tuesday.

I have not done that!

Well, last Monday I thought that Q designated the transfer, solely by
thermal means, of energy from A to B by virtue of a temperature
difference. Example 3 above is inconsistent with this definition. Anybody
who wants to claim consistency of the conventional interpretation is in big
trouble -- I claim you can't be conventional and consistent at the same
time. That has been my main point all along. Joel's attempt to be
consistent has led him to give an unconventional definition of Q a few
paragraphs back.

And we don't bother to distinguish the form of arrival in B as we lump it
all together and call it Delta E.

Again, that's unconventional. Unless/until I see evidence to the contrary,
I will continue to believe that there is no consistent conventional
interpretation of the W+Q equation.