I'm finding this discussion very helpful. Thanks to those of you responding
to my comments.
I think John's comment that "thermal energy" is tricky, is quite true. I am
still trying to decide what counts as thermal and what does not, and
therefore what it means to thermalize something. I am also trying to
understand which interactions are internal and which interactions are
external.
At this point we have John saying bulk rotational energy cannot be
thermalized without an outside interaction. We have Bob saying it happens
all the time and he invokes entropy arguments. And Hugh is making some
points about my solar system model that I don't know how to answer.
Here is some progress I have made, along with some more questions.
John's reminder that we can connect bulk rotational energy to angular
momentum about the center of mass is agood one: rotational KE = L^2/2I.
I guess I was thinking that thermalization would include transfer of bulk
rotation about the center of mass into rotation of individual components.
But if angular momentum is conserved (because of no outside interactions)
then the total L^2/2I doesn't change. John is saying this with an equation
and Hugh is saying it with words. So I think both are convincing me that
condensation of rotating matter into a solar system is not a thermalization
process. It fits my earlier criterion of the passing of gross bulk motion
into motions of the parts, but it does not fit the criterion of random.
So, is that the key here? Thermalization is not just the transfer of
macroscopic motion into microscopic motion... but also requires the
microscopic motion be random? If so, I can live with that, but I am not
sure I was alone in viewing simple transfer from macroscopic to microscopic
as a thermalization process.
Wouldn't another criterion for something being "thermalized" be whether the
process could be reversed? Once angular momentum has distributed itself
from the bulk rotation of the cloud to rotations of individual planets, can
it go back to the bulk again? I guess it can do that when the star goes
supernova. But does that count? That is, are there other mechanisms to get
us stop the rotations of the planets and moons so that all rotational energy
is back to revolutionary.
Note I am using two astronomy terms here to help me describe what I am
trying to say... I am using rotation to mean the rotation of a planet or
moon about its own axis, and I am using revolution to mean motion around the
center of mass of the whole solar system. There ought to be a third term
for revolution of moons about a planet, but I don't have such a term in my
vocabulary.
Anyway, if gravity drives the formation of a solar system from a revolving
dust cloud, and some of the revolutional momentum and energy goes into
individiual rotations, then can that process reverse, short of supernova?
If not, does that mean thermalization has occurred, or is that not a valid
way to describe thermalization.
Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817