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Re: Thermal Energy - thermalization of rotational energy



I have a couple ideas/questions I would like to share. If some of you have
disagreements with me I might be changeable... I am still working through
this.

* * Thermal energy and thermalization * *

I am most comfortable saying thermal energy is (f/2)kT.

As for thermalization, let's ignore relativity and just view things in my
rest frame. I would say an object is thermalized in my rest frame when
(f/2)kT is the only energy it has. I think I also assume thermalized
implies we have a thermal equibrium in which rotational, vibrational,
translational components are not out of whack with each other. If I know
the temperature and the accessible modes of motion, then I know the amount
of rotational, vibrational, translational energy.

When I was working in the fields of nuclear physics and nuclear detectors
the word "thermalized" cropped up quite a bit. Accelerator beams would
enter the beam dump and become thermalized. Fast neutrons from a reactor
would become thermalized. Particles would enter a detector and become
thermalized. I believe this is very common language.


* * Internal Energy * *

I think it is okay to define "internal kinetic energy" as sum-of(1/2 m
v(cm)^2). This doesn't mean I necessarily see great utility in it... it
just means I am okay with the definition.

Perhaps I'm slower than others, but the realization came pretty late to me
that defining internal kinetic energy this way can yield a very different
result than (f/2)kT. Basically I am saying that it was a fairly recent
revelation that internal energy defined this way would include bulk or
non-random rotational energy. I don't know why this came so late... it just
did.


* * Relation betweeen Internal Energy and Thermal Energy * *

Prior to my revelation about rotational energy I wasn't bothered very much
by people who equated internal energy with thermal energy. Now I am
bothered a great deal by it.

This was why I jumped on the golf-ball question. Knowing that some people
equate internal energy to thermal energy, and knowing that flying golf balls
spin, anyone who equates internal energy to thermal energy would have to say
the flying/spinning golf ball would have greater thermal energy than it had
when sitting on the tee.

There is no way I would say that, but I was pointing out that anyone who
equates internal energy to thermal energy, and then says the flying/spinning
golf ball has the same thermal energy as it had on the tee, has some major
consistency problems.

* * Thermalization Processes * *

In the themalization processes I described above, the object with greater
energy than predicted by (f/2)kT reduced its energy to (f/2)kT' by
interaction with objects already in equilibrium at (f/2)kT. I began to be
bothered by the idea that the bulk rotational energy of an object cannot be
thermalized by the object itself.

Why? Because 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 motion unless we
assume the universe began with zero angular momentum. Perhaps some are
comfortable with the idea the universe has no net angular momentum, but I am
not sure we can say this with any confidence. If the universe is headed for
a thermal equilibrium in which T is not zero, we seem to be comfortable
saying there is net energy; so why not net rotational energy? But if there
is net rotational energy, and if it is not possible for a system to
self-thermalize bulk rotational energy, and bulk rotational energy is not
thermal energy... then the universe is not headed toward thermal
equilibrium.

It seems to me we observe processes in which gravitational interaction
between bodies allows conversion of bulk rotational energy to kT energy.
The major heating of Io by Jupiter, or the more subtle heating of Earth via
tides are examples.

* * This is where I'm at * *

I find these questions interesting and that is why this discussion is
intereting to me. I am not necessarily trying to invent new language or new
ideas. I am just trying to understand how others view these issues and what
language is appropriate as we discuss these issues.



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