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Re: thermal energy



PS Some want to call the translational KE alone the thermal energy because
this is what is used in the simple thermo calculations -- but still all
this is unnecessary and usually confusing.

.................................

For an ideal gas the only energy of concern is the "internal energy" --
some people sloppily call this "thermal energy". For a real gas or other
system the "internal energy" is comprised of the kinetic energy of
molecular motion and the various binding and attraction energies of and
within the molecules-- all these are potential energies and are usually
bundled into a single potential energy for thermo analysis.

Some people want to confuse things by calling all of this energy (ie the
internal energy) -- or just the kinetic energy of motion -- "thermal
energy" - but all that is quite unnecessary and usually unhelpful.

We already have perfectly good language for these concepts -- why muck
around with it?

Jim Green

At 12:26 02 03 2000 , you wrote:
Hello,

I have a question on concept of thermal energy. I'd like to have a solid
definition for it. Here are some quotes:

1) Fundamentals of Physics (Halliday, Resnick & Walker), 4th edition, p. 188

".., thermal energy, which is associated with the random motions of atoms
and molecules in a body,..."

Later in the text thermal energy is used as a synonym for internal energy.
Giancoli's Physics follows the same convention. It may be appropriate in
the introductory course but I suspect that there must be a difference in a
closer analysis as the next quotation suggests.

2) Teaching Introductory Physics (Arnold B. Arons), p. 147

Arons lists different internal energy changes:

(a) Internal thermal energy change
(b) Internal chemical energy changes
(c) Internal kinetic energy change (includes translational and rotational
energy changes)
(d) Internal potential energy changes (three types)
(e) Miscellaneous internal energy changes (e.g. sound, radiation)

What could Arons mean by thermal energy here? I have thought that thermal
energy could be another name for type (c). Fundamentals of Physics seems
to hint into this direction in the quotation above.

Molecules have vibrational energy as well. For some reason Arons doesn't
include this into his classification. BTW I think that Arons' book might
be the best book written on physics education.

Any suggestions?

Regards

Antti Savinainen
Physics teacher
Kuopio Lyseo High School/IB-section
Finland

Jim Green
mailto:JMGreen@sisna.com
http://users.sisna.com/jmgreen