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Re: CONSERVATION OF ENERGY

On Tue, 29 Jul 1997, Jim Green wrote:

At 05:57 AM 7/29/97 -0400, Gene wrote:
I would like to get a few things straightened out concerning internal
energy--like what is it.

I am thinking that this question is too narrow -- It is a good question of
course for spending time on phys-l ranting about words, but, to have a
meaningful discussion, first you should say what the system is and what
formalism you are going to use the concept in and for what purpose.

If you are going to use the First Law, you will also want to ask what "Q"
and "W" are. And then if you want to include any more than "random" motion,
you will need a good reason to do so. It can be done (and Leigh will want
to), but the *usefulness* for doing so escapes me.

IE there is not much point in specifying "internal energy" in some
intergalactic formal sense for all time and space unless the rest of the
problem is illuminated.




Jim Green
JMGreen@sisna.com





Jim,
The rest of the situation is illuminated! Consider the case
which has already been mentioned in this thread. A heavy cylinder is
filled with a mixture of gasoline and air sealed and insulated. In the
side is a spark plug to which we can apply a spark whose energy
contribution may be considered negligible. The temperature goes up when
the plug sparks; the pressure increases; but no heat is transfered, no
work is done, and there is no change in internal energy. In order to
understand how this can be we have to include all of the energy in the
internal energy.



W. Barlow Newbolt 540-463-8881 (telephone)
218 Howe Hall 540-463-8884 (fax)
Washington and Lee University newbolt.w@fs.science.wlu.edu
Lexington, Virginia 24450 wnewbolt@liberty.uc.wlu.edu

"What can you say about a society which insists that
God is dead, but which also insists that Elvis Presley
is alive?"
Irv Cupsinet