Several people have written to say that they don't buy my argument that a
rail car coupling must include a spring and a shock absorber. People seem
to assume that these are needless complications. They demand a simpler
description.
Please consider the following arguments:
Argument 1) Assertion: Any simpler description is unphysical. Trust
me. (Yeah, sure, that argument works every time :-)
Argument 2) Physics: There are compelling physical reasons why dissipation
is necessary and cannot be well approximated by a simple nondissipative
model. See previous notes for details.
Argument 3) Real-world data: If you won't accept the physics argument, how
about some engineering data? It appears that real-world rail cars obey the
laws of physics!
It was easy to predict that rail cars couplings *must* have devices
containing springs and shock absorbers, but until a moment ago I had no
idea what they looked like, how they worked, or what they were
called. Well, it took 5 minutes of AltaVista work to discover that they're
called draft gears. Specifications and nice cutaway drawings can be found at http://www.cardwest.com/draftgears.html