Re: ENERGY WITH Q

[kowalskil <kowalskil@MAIL.MONTCLAIR.EDU>]

THANK FOR YOUR HELP AGAIN, JOHND.
"John S. Denker" wrote:
> At 07:00 PM 10/22/01 -0400, Ludwik Kowalski wrote:
> > One can declare that S=0 at T=0 (an arbitrary reference level,
> > like for PEgrv) and observe that S is always positive.
>
> I would not recommend declaring this, since it's not true.
> S is not arbitrary.  S is not generally zero at T=0. That's
> a fact, and piling up a large number of high-school physics
> books that say otherwise isn't going to change this fact. ....

I should have resisted the idea of introducing entropy
into MY OUTLINE on the basis of not having classroom
experience with this topic. The topic is important; how
should it be introduced (and how much time should be
devoted to it) in the first physics course is not clear
to me. Is the following acceptable?

------------------------------------------------------------
Heat generated through friction, H, is always positive, it
leads to an increase of Eth at the expense of Emech. This
offers an opportunity to introduce entropy (dS=H/T) whose
unit is J/K. The positive sign of H (in experiments discussed
with Model 2) shows that dS can not be negative. The natural
tendency of S to increase can be illustrated with numerous
examples without making a reference to the idea of non-
reversibility of dissipative processes.

The entropy of the universe is increasing, even when chemical
reactions are ignored. In my opinion "latent heat" is like
chemical energy. The concept of S is worth revisiting (also
superficially) in the context of Model 3. More advanced
considerations should be addressed in a dedicated course.
------------------------------------------------------------
Referring to:
> > This offers an opportunity to introduce entropy
> > (dS=H/T) whose unit is J/K.

John D wrote:

> This is unsatisfactory for two reasons. Obviously, this
> causes trouble when T=0. What's worse, at the point where
> this was introduced, Ludwik's exposition has not provided
> a sufficiently-clear distinction between thermal energy and
> nonthermal energy. We were looking forward to getting one.

Troubles with singularities are possible elsewhere, for
example, in Coulomb's law.

Thermal energy is associated with several kinds of random
motion at the molecular level. Why is this not sufficient
in the first physics course? I think that the monoatomic
gas topic provides a sufficient illustration of what is
behind thermal energy.
Ludwik Kowalski