Re: macroscopic vs microscopic degrees of freedom (was: why pseudowork (NOT)

[Leigh Palmer <palmer@SFU.CA>]

> On Fri, 29 Oct 1999, Joel Rauber wrote:
>
> > If my 1993 Geo metro is rotating as well as translating (as it has been
> > known to do on the icy roads of South Dakota), the energy associated with
> > that rotational motion is in what category? internal energy?
>
> In the context of our paper, we put it in the category of internal energy.
> We thought long and hard about this and decided that it made life, in that
> context, easier. We fully recognize that there are other useful ways to
> proceed.

In what follows I ask only rhetorical questions, so I have supplied
my answers in parentheses

Consider the example I provided earlier. I paddle my canoe. The water
is churned on a scale comparable to the size of the paddle, and the
turbulent motion then evolves to smaller scales over an interval of
time measured in seconds. What part of the work which was done on the
water (and I will argue that work was done on the water) goes into
mechanical energy and what part goes into internal energy? Does that
fraction vary with time? (yes)  Does the amount of work which *was*
done on the water also vary with time? (obviously not)

Would work, by any definition, be a useful quantity to employ in a
calculation having to do with the evolution of this system? (yes, but
only the thermodynamic kind)

I think that whenever work gets hard to define one should not try to
use the concept. Such efforts always remind me of the sort of "ad
hocery* that used to characterize explanations of phenomena which
employed the caloric model. They were often clever, but there was
lttle or no general value to them. (Some were wrong, of course.)

Leigh