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Re: [Phys-l] Configurational energy



Although there is no configurational energy associated with
intermolecular interactions for an ideal gas, there is still
configurational energy associated with intramolecular interactions. Not
all of the molecules are in their ground states. There can be exchanges
of energy between molecules during collisions.

Limiting configurational energy to intermolecular forces is precisely
the restriction I mentioned in my original post.

Daniel Crowe
Loudoun Academy of Science
dan.crowe@loudoun.k12.va.us
jsd@av8n.com 10/17/07 6:26 PM >>>
In the context of:

Consider the thermally-isolated gas cylinder as shown on the
left of this figure
http://www.av8n.com/physics/img48/locrian.png

If I express the energy of the system as a function of the
position of the piston, is that a kinetic energy and/or a
potential energy and/or a configurational energy?


On 10/17/2007 05:22 PM, Dan Crowe wrote:

The short answer to John's question regarding the piston is "none of
the above". It's a combination of kinetic and potential energy (aka
configurational energy).

I am surprised by that answer. I cannot imagine what it means.
Does it refer to a 50/50 combination of kinetic and potential,
or some other combination?

The gas is considered ideal. The piston is moved only gradually,
never suddenly. (These idealizations often hold to high accuracy
in practical situations.)

*) Therefore 100% of the energy is kinetic, if you look at the gas.

*) Meanwhile, if you look at the piston, 100% of the energy is
determined by the position of the piston.

*) To be explicit, 100% of the energy of the system is kinetic, and
is determined by the position of the piston.

I cannot imagine any value other than 100% to plug into these
statements. For example, plugging in 50% would not be an improvement.

Changing the terminology from "potential" to "configurational"
does not change the main idea of this puzzle AFAICT. The idea
is insensitive to terminology (as is so often the case).

John and I will have to agree to disagree on the usefulness of trying
to
improve the terminology of physics. I continue to think that it is
worthwhile, and I will continue to try.

Let us know how that works out.

A couple dozen candidates for improvement are listed at
http://www.av8n.com/physics/weird-terminology.htm

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