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[Phys-L] equipartition ... was: phase change



Executive summary: It's energy per *quadratic* degree
of freedom.

On 02/25/2016 10:32 AM, Carl Mungan wrote:

So equipartition doesn’t apply?

There are a lot of misconceptions about equipartition.
The explanations you see in introductory books are often
grossly incorrect.

For starters, ask your students why a particle in a
parabolic potential (i.e. a harmonic oscillator) has
both KE and PE contributions to its heat capacity,
whereas a particle in a square-well potential (i.e.
a particle in a box) has only KE.

It's the same particle in both cases, but the two heat
capacities are markedly different.

Next question: What happens if we split the difference,
i.e. if we have a container with slightly rounded corners
and slightly sloping sides, so that it is not quite as
curvy as a parabola, yet not quite as square as a box?

This is directly relevant to part of the phase-change
question, because even though the particles are the same
in the gas as in the solid, their PE environment is quite
different.

The explanation, with diagrams and equations, can be
found at
https://www.av8n.com/physics/thermo/equipartition.html
especially
https://www.av8n.com/physics/thermo/equipartition.html#sec-interpolate-equipartition