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Re: [Phys-l] teaching energy

Did you try the experiment?

bc, who certainly knows, not.

p.s. allow means at its "natural rate", i.e. limited only the "spring" force and its mass.

R. McDermott wrote:

----- Original Message ----- From: "Bernard Cleyet" <>
To: "Forum for Physics Educators" <>
Sent: Friday, September 29, 2006 11:50 AM
Subject: Re: [Phys-l] teaching energy

"The analogy to the rubber band is a visual example: The band
changes its geometry as you stretch it, and energy resides in that altered
geometry. Allowing the band to return to its "natural" geometry releases
the energy."

Not a good example except in the "mind's eye"

Try this experiment:

W/ a high quality very large rubber band Stretch it and hold 'till
equilibrium. Then using your lips as a thermometer (hold gently
against one) allow the band to relax. If you are releasing it's
energy it should warm, right?

I would expect that if there was no other object interacting with it, yes, but since you are forcing this release to proceed slowly (presumeably by holding it with your hand), it would seem reasonable to me that at least some of the energy in the band would be showing up in your hand(s), thus reducing any observable heating of the band itself. Not to mention that the time involved in the release allows energy to be transferred to the air as well. You would also need to consider whether or not the energy is sufficient to register on your lip as heat in the FIRST place. Is short, I'm not sure this is a convincing refutation of the model.
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