I think that my question was not well enough formed: I am looking for
another thermo example similar to the classical frictionless piston and
cylinder. I want to walk gingerly because I don't want to start another
battle over the First Law. That is not scheduled for another eight months. <g>
I am not sure that the elastic properties of an "ideal" material will work
-- I am still thinking.
I need a process where deltaS=0 just as for the cylinder, but (likely due
to senility) I can't think of one.
The spring/steel bar/rubber ball looks ok but I don't know how to calculate
deltaS for these cases.