At 07:57 AM 11/25/99 -0500, Ludwik Kowalski wrote:
>Thermodynamics of energy storing objects (such springs,
>chemical compounds or sources of emf) is a much more
>advanced topic than a typical chapter on elasticity.
Agreed. You can't teach everything at once. In a typical syllabus, basic
notions of elasticity are introduced before thermodynamics.
> We do
>not speak about the equation of state of steel while describing
>its behavior in terms of elastic moduli.
...
> we simply
>observe that, in the first approximation, L=Lo*(1+alpha*dT).
>We do not say that this is a state equation.
It depends on what you mean by "we", Kemosabe.
By the time both elasticity and thermo have entered the discussion, then
all the points you mention can be (and sometimes are) made; see e.g. _The
Feynman Lectures on Physics_ volume I figure 44-2.
>That is why I think that Socrates had no right to ask the
>fictitious H.S.S. character for a numerical comparison
>between the potential energy stored in a chemical compound
>and in a compressed spring. It was not a fair question.
>Seeing the analogy was already a big accomplishment.
But once the analogy has been seen, the numerical part of the comparison is
so easy that there's nothing to lose by asking for it. Indeed even if the
analogy is *not* grokked at the level of deep physics, the point can be
made at the level of dimensional analysis, and the numerical comparison can
be easily made.