Here's one more point about whether the energy is "internal"
or "external".
We associate gravitational potential energy (m g h) with an
object of mass m at height h. A similar equation applies to
electrostatic potential energy of a charged object.
The question is, what does it mean to "associate" an energy???
a) There is one school of thought that says the gravitational
potential energy is "internal" to the object.
b) There is another school of thought that says the energy
actually resides in the gravitational field, and is therefore
almost entirely external to the object.
Approach (a) seems to be common at the high-school level,
while approach (b) seems to prevail at the more advanced
levels.
Similar words apply to the electrostatic version, although
approach (b) is even more strongly favored. Poynting had
something to say about this.
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The intriguing thing is that for most purposes, it doesn't
actually matter whether the energy is considered internal
or external. To an excellent approximation, the equations
of motion (including the principle of virtual work) don't
care where the energy resides.
It would matter if you ever measured the energy density of
the field (perhaps by setting up a Keplerian orbit around
the field, since the orbital period depends on the amount of
mass i.e. energy inside) ... but that is rarely (if ever!)
done. Feynman has a long discussion of this issue, namely
the puzzle over where the energy resides.
This a sufficiently well-known puzzle that whenever you
see a document such as http://www.physicsclassroom.com/class/energy/u5l2a.cfm
ranting about the importance of the internal/external
distinction, you know immediately that they haven't
thought about the issue at all.
Also the idea that there could ever be a correspondence
that maps "internal/external" to "conservative/nonconservative"
is dead on arrival --- another proof that they haven't
thought about the issue at all.
It remains a mystery why anybody would go to the trouble of
inventing new and heretical versions of the basic concepts
of physics. What is wrong with the plain old conventional
notions of energy, conservation, et cetera? And wouldn't
you think that somebody who invented a new version would
feel obliged to check whether it was consistent with the
known facts?