Re: Thermal Energy - thermalization of rotational energy

["John S. Denker" <jsd@MONMOUTH.COM>]

Michael Edmiston wrote a long discussion followed by:
> ... I don't know how to bring this into agreement with some other
> ideas.  In my case these other ideas happen to be astronomy ideas.
>
> The idea that the universe is heading toward thermal equilibrium would be
> inconsistent with the non-thermalization of bulk rotational energy

1) Bulk rotational energy can be thermalized, even without
outside interaction.  Imagine a bola, the Argentine lariat
with balls attached at the end.  Set it spinning in outer
space.  Now imagine that in the middle I have a reservoir
of extra string, and I gradually pay it out, using a tiny
windlass or whatever.  The centrifugal tension in the string
does work on the windlass during this process.  I choose to
dissipate this energy, thermalizing it in the brakes in the
windlass.

Something along these lines has practical application:  There
is a nasty tendency for satellites to tumble.  But if you put
in a shoshy liquid, it will thermalize the bulk rotational
energy, stabilizing the rotation around the axis of largest
moment of inertia.

2) In the opening words of his book on statistical mechanics,
Feynman defined thermal equilibrium as <<when all the slow things
have happened, and the fast things have not.  The gas in a
piston will eventually erode away the container, but long before
that happens it will have reached a state of definite temperature,
pressure, et cetera>> (approximate quote;  I'm far from my books
at the moment).

Violation of conservation of angular momentum certainly
qualifies as a slow process -- vanishingly slow.  So if a
system has no coupling to the outside world (so that its
angular momentum is conserved) and if it has an upper bound
on its moment of inertia, then (and only then) there is a
certain amount of energy that will never be thermalized.
But this really tells us nothing about the behavior of
energy;  it is the conserved momentum that is controlling
the situation.

3) A word of caution:  People have implicitly, and sometimes
explicitly, equating thermal energy with internal kinetic energy,
or random internal kinetic energy, and things like that.  Be
careful, the word "kinetic" does !!not!! belong there.  We can
have thermal potential energy, too.

There have been waaaay too many textbook discussions of thermo
using ideal gasses as the only illustration.  In an ideal gas,
_all_ the energy (thermal or otherwise) is kinetic.  But in the
other 99.99999% of the world, we have other forms of energy, and
they get thermalized, too.