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Re: "Dissipation" (was Re: momentum conservation(2))



On Wed, 15 Mar 2000, Tim Burgess wrote:

The PASCO carts, I think, have a significant amount of what you call
"dissipated" energy in the form of potential energy that "locks" the
two carts together. The "velcro" strips between the carts do this.
To test my idea you could take the locked carts and carefully (with
one stationary) pull one away from the other with a thread. You will
find that once the cart "tears free" it is launched with a small
velocity. Measuring the velocity of this "launched cart" may reveal
a major portion of your energy labeled as "dissipated". Just an idea.
Hopefully I'm not muddling this too badly. (The pull is like an activation
energy in Chemistry).

Velcro in its intended use does not store any significant amount of
potential energy. When two carts equipped with velcro collide, the "lost"
kinetic energy is indeed *dissipated*, not transformed into potential
energy of bent velcro barbs. If you find that the cart is launched with a
small velocity after being torn free, it is simply because you were
exerting a force on it in order to tear it free and *kept* exerting that
force for a short time *after* it broke free.

John Mallinckrodt mailto:ajm@csupomona.edu
Cal Poly Pomona http://www.csupomona.edu/~ajm