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Re: COLLISION



At 09:37 11/26/99 -0500, David Abineri wrote:
When a moving railroad car collides with a stationary car of equal mass
elastically, the one car stops and the other begins moving with the same
velocity as the first.

If they now collide inelastically by coupling together, half of the
kinetic energy of the system is lost.

Now, my concern is, where has the kinetic energy 'gone'? Certainly air
was moved, sound was created and deformations took place but surely all
this happened in the elastic collision too.

Why should there be such a significant difference in the accounting of
energy between these two systems?

Any help would be appreciated.

--
David Abineri dabineri@choice.net

I rationalize the result in this way.
It is certain that in an elastic collision, some energy is indeed
lost - a small part of the whole, which it is convenient to ignore.

In David's inelastic situation, I can represent the coupling by a
flexible thread of some length, so that when truck 1 hits truck 2,
truck 2 begins to move off, until the tether goes tight, at which
time the situation is functionally equivalent to the first collision.
Truck 2 moves, and truck 1 halts.
This situation continues losing a modest proportion of the total
energy at each cycle until it is dissipated.

This thread may be conceptually replaced by the coupling mechanism,
to the same effect.

You will see some slight resemblance of this story with the comparable
puzzle: where does half the energy go when a charged cap is connected
to another simlar device? (As heat or oscillatory radiation)



brian whatcott <inet@intellisys.net>
Altus OK