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Re: heat is a form of energy



If we find it useful to teach that macroscopic objects, like air-track
gliders, can "have or possess" something called translational kinetic
energy... and if we find it useful to teach that macroscopic objects,
like wheels, can "have or possess" something called rotational kinetic
energy... then it seems we also can say that microscopic objects, such
as atoms and molecules, can "have or possess" translational and
rotational energy.

I put the words "have or possess" in quotation marks to indicate that
some of us feel more comfortable with energy as a useful "concept" or
way of describing things as opposed to a "something" that objects can
"have or posses." Let's not argue that. My point here is that
whatever view we have of the translational and rotational kinetic
energy of macroscopic objects ought to be applicable to atoms and
molecules... especially in the simplistic view that atoms and molecules
are just very small masses. So please just give me that for a moment.

If you'll tolerate that, then we need to decide whether we want to
ascribe any special name to the kinetic energy that atoms and molecules
have "internally." Here, internally just means energy "possessed" by
the individual atoms and molecules that can be identified as separable
from any kinetic energy associated with the center of mass of the
entire object.

So, what do we want to call this? Thermal energy? Heat? Internal
kinetic energy? Something else?

And we also realize that when objects have a different "average
internal kinetic energy" we have become accustomed to saying they have
different temperature. But if we allow these objects to come into
contact along some interface, then the collisions at the boundary allow
kinetic energy and momentum to be passed across that boundary. And
given sufficient time, objects that started with different average
internal kinetic energy can "pass net energy" across the boundary until
the lower one gains sufficient energy and the higher one loses
sufficient energy that they are no longer different.

What are we going to call this process? Heat flow? Thermal energy
transfer? Something else?

I hope some people are not advocating that we completely throw out this
"kinetic theory" view of what's going on microscopically, because I
sure find it useful, and it's not too hard to teach. But as long as
we're allowed to find this useful, and then to use it, I guess I don't
care what we call it.

I personally prefer thermal energy and thermal energy transfer. But I
guess I don't feel to bad about heat and heat flow. Someone already
pointed out that the concept of heat (at least the word "heat") still
has substantial use in the public. Therefore, especially when we teach
general education physics, it seems to me it is our job as scientists
to help the public understand the implications of their words. Thus,
if the public wants to use the words heat and heat flow, then I don't
feel it nearly so important that we try to change that, as much as I
feel it is important that we help them understand what they're talking
about. In that regard I don't have much problem telling them that they
are talking about the motions/rotations of the atoms and molecules, and
that heat is the total amount of that going on, and temperature is
average amount of that going on. I tell them that I prefer the words
"thermal energy" over heat, but I'll let the general public stick with
heat if they want to. Otherwise they just get mad or frustrated with
science and scientists. And goodness knows we've had enough of that.

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