Re: Conservation Laws

[John Mallinckrodt <ajmallinckro@CSUPOMONA.EDU>]

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

> 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.

Totally inelastic collisions *always* involve dissipation.  When a moving
rail car couples to a stationary one, at least a megagoogob of energy is
dissipated and much of it ends up as internal energy of the rail cars.  In
fact, it is only systems--like rail cars--that have internal structure and
are, therefore, capable of storing internal energy that *can* have
inelastic collisions.  As I recall, some of the earliest evidence for
quarks was the observation of inelastic scattering of electrons off of
nucleons. This observation was taken to imply that the nucleon was able to
dissipate energy into internal modes that would not exist if it did not
have structure.

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