Re: CONSERVATION OF ENERGY

[twayburn@juno.com (Thomas L Wayburn)]

On Tue, 29 Jul 1997 08:03:13 -0800 (PST) John Mallinckrodt
<ajmallinckro@CSUPomona.Edu> writes:
> A writes:
>
> > John Mallinckrodt writes:
> >
> > > We need to 
> > > distinguish between reversible and irreversible heating.  Both are 
> what 
> > > I would call "thermal" processes but only the second kind involves 
> > > "temperature differences."  Yes, a little picky. 
> >
> > Yeah, because an infinitesuimal temperature difference is still 
> > a temperature difference (as shown by nonstandard analysis).   
> > Infinitesimals work.
>
> Ah, but because you read what I *actually* wrote rather than what 
> I *meant* to write, you have misunderstood me.  (I hate it when 
> that happens.) I *meant* to say "only the *first* kind involves 
> "temperature differences" since, in "irreversible heating," the 
> interface separates regions that have *no* defined temperature 
> and, thus, no temperature *difference.*
>
> John
> -----------------------------------------------------------------
> A. John Mallinckrodt      http://www.intranet.csupomona.edu/~ajm
> Professor of Physics    mailto:ajmallinckro@csupomona.edu
> Physics Department       voice:909-869-4054
> Cal Poly Pomona            fax:909-869-5090
> Pomona, CA 91768-4031   office:Building 8, Room 223
Well said, John.  Maybe this could be an opportunity to turn the
discussion to what I really care about.   Now the sun behaves like a
blackbody radiating at 6000 K, so let it be that.   The earth is nearly
an isothermal system at 300 K with an emmissivity of about 0.8, say; so,
let it be - let it be.   Now, the sun surely transfers energy to the
earth and in a highly irreversible way, but the temperatures are
well-defined bei mir.
Right?   Is this heat?  Is it work?  Is it a flow of availability?
entropy? enthalpy?  Photons have some characteristics of particles, e.g.,
momentum?  How much availability, H - T(surr)S, enters the control volume
consisting of the earth and its atmosphere?  How much availability is
lost during this process?   How much more work could have been done if
the availability that left the sun (and was aimed at the earth) had been
transferred to the earth reversibly?   Consider John's statement, "... 
in "irreversible heating," the interface separates regions that have *no*
defined temperature and, thus, no temperature *difference.* "   Does the
sun heat the earth?
Is the heating irreversible?   Is the temperature defined?    Please
explain this to me because I have made myself sick worrying about this.  
(I'm better now.)

Thanks / The Amateur