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Conservation Laws



In the Candide-like world of physics storerooms there are rigid weightless
rods, point masses, frictionless surfaces and totally inelastic collisions
as well as other oddities. My problem is with the mutual exclusivity of the
conservation of momentum and conservation of energy laws. Consider a moving
rail car and a stationary rail car on the same frictionless, horizontal
rails. The moving car strikes and couples to the stationary one in a
totally ineleastic fashion. No dissipative forces are about. 'Tis indeed a
closed, conservative system. Yet the final speed of the coupled pair is not
the same using the two laws. If indeed this is the best of all possible
worlds, why do not the speeds from the two calculations agree?

"An education isn't how much you have committed to memory, or even how much
you know. It's being able to differentiate between what you know and what
you don't know" -- Anatole France.
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