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Date: Thu, 24 Jul 1997 01:27:57 -0700
From: Leigh Palmer <palmer@sfu.ca>
.... Too much meaning is being heaped upon the word "internal". Some
discussants want this to be something which remains within the physical
boundaries of the system. ... Some want only to count "thermal" energy,
a fallacy well treated in John's note. The truth is that in classical
equilibrium thermodynamics there is only one kind of energy, the internal
energy of the system. .....
This term is not in my dictionary, nor should it be in that of any
physics teacher. It is a source of confusion ... and a barrier to
conceptual grasp."
... consider a ... situation in which a large chunk of matter is struck
and then vibrates in a complex and macroscopically observable manner.
Let's think about how we would apportion its internal energy between
mechanical and thermal components. We can (in principle) do a spectral
analysis to determine the amount of vibrational energy in each vibrational
mode. But where do we cut off the sum? ... I simply don't see any rational
way of deciding how much of the internal energy here is "mechanical" and
how much is "thermal." ... My conclusion from considering such examples
has been that we should not deceive ourselves into thinking that internal
energy can be divided into thermal and mechanical portions.