Re: Thermo of Springs/Sidebar

[John Denker <jsd@MONMOUTH.COM>]

At 11:47 AM 11/25/99 -0700, Jim Green wrote:
> Well, an ideal spring is ideal; the temperature of a real spring does
> change upon flexing.

That depends on a particular notion of "ideal", which depends in turn on
what sort of task one is doing.  In subsonic fluid dynamics, it is often
helpful to approximate the fluid's density by a constant.  For Carnot-cycle
thermodynamics, such an approximation would be distinctly unhelpful.  If
you choose to neglect the temperature coefficient of the spring, that
precludes any possible thermodynamic analysis -- but that is merely a
choice not a statement of fundamental physics.

> But my question is whether there is _any_ example of a macroscopic
> reversible process other than the ideal piston in a cylinder.
>
> Isn't it odd that the entire basis for classical thermodynamics (or,
> better, thermostatics) is that cylinder.
>
> What have I missed?

1) Springs are missing iff they have been arbitrarily ruled out.

2) What about the thermodynamics of chemical equilibrium?  pH and pKa and
all that?

3) What about the thermodynamics of charging a battery?

4) What about the thermodynamics of a dilution refrigerator, e.g. the
venerable Electrolux cycle, or the 3He-4He dilution refrigerator?

5) Perhaps simplest of all, what about the thermodynamics of an adiabatic
demagnetization refrigerator?