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I don't see why this is an issue. "Energy" is an abstract quantity, not a thing-in-the-world. You can say it "resides" wherever you like. Can you design an experiment that favors one view over another? Or a problem that can be solved if you hold one of those beliefs but not the other? This seems to me to be philosophy or psychology, not physics. [Not to bring this issue up again, but it also seems like philosophy/psychology when we debate whether the force causes the acceleration of the acceleration causes the force.]
As for the earlier question: I think I know why it is important to distinguish between conservative and non-conservative forces, and think I can design an experiment to see if a force is conservative. But I have no understanding at all of the terms "internal" and "external". I'd never seen them before this thread started and I can't imagine teaching them. I don't even make a big deal about "contact" vs. "non-contact" forces -- in the end, aren't all forces "at a distance"?
-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
bounces@carnot.physics.buffalo.edu] On Behalf Of William Robertson
Sent: Wednesday, December 15, 2010 1:14 AM
To: Forum for Physics Educators
Subject: Re: [Phys-l] internal/external conservative/nonconservative
forces!?!?
Stating that the energy properly ascribed to a system resides instead
in one object of the system is not an approximation. Rather, it is a
small lie. Small lies are fine as long as we explain to students what
the lie is, and why it's okay to proceed with the small lie. And here
I am not talking about using mgh rather than the universal law of
gravitation.
Bill