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Re: [Phys-l] thermal energy



Fine--but in the particular case in point, we were talking about a gas, and the 'random' is part of the temperature definition ( yes, that should be 'for an ideal gas') so was implied to go with the heat part. So, in context, I don't think 'roughly' was inappropriate. ;-)

;-)

Rick

----- Original Message ----- From: "John Denker" <jsd@av8n.com>
To: "Forum for Physics Educators" <phys-l@carnot.physics.buffalo.edu>
Sent: Thursday, December 04, 2008 12:59 PM
Subject: [Phys-l] thermal energy


On 12/04/2008 07:19 AM, Rick Tarara wrote:
The thermal energy (heat) is roughly the
measure of the total kinetic energy of all the molecules.

I wouldn't say that, not even "roughly".

1) It would be better to add the word "random". A cold,
fast-moving bullet has lots of kinetic energy that must
not be counted as part of the thermal energy.

2) It would be better to remove the word "kinetic". In a
solid, very nearly half of the thermal energy is kinetic
energy and the other half is potential energy. Hint:
treat thermal phonons as harmonic oscillators.

In this regard, solids differ from ideal gases. But there
is more to physics than ideal gases.

This is a very common mistake, but it's still a mistake.
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