Re: Conservation Laws

[Richard Bowman <rbowman@BRIDGEWATER.EDU>]

On Mon, 13 Mar 2000, E.C. Muehleisen wrote:

> 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?

There is energy dissipated in the form of heat and deformation. For one
things the latches on the two rail cars must be closed to hold the two
cars together, plus some energy is used to heat the cars up as their
frames are depressed due to the collision and then rebound after the
collision. So mechanical energy is not conserved but total energy is
conserved.

Richard
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Dr. Richard L. Bowman
Chair, Dept. of Physics                  e-mail:  rbowman@bridgewater.edu
(and Dir. of Academic Computing)                     phone:  540-828-5441
Bridgewater College                                    FAX:  540-828-5479
Bridgewater, VA  22812               http://www.bridgewater.edu/~rbowman/
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