I think that most members on this let believe that physicists work with models of the world out there; all of which are approximate. I think it is important for purposes of discussion, that arguments be based on some particular model; such as Newton's Laws, Newton' Law of Gravitation, or the four Laws of Thermodynamics, etc. Otherwise, arguments have no end. Trying to be "realistic" to the tiniest detail will not work and all arguments end up going off on tangents. One may start with Classical Mechanics and before too long it becomes quantum field theory or string theory or general relativity or something else; all of which will be beyond the starting model. We can study rigid bodies and later elasticity and later foam or other things, just not at the same time. After all, we do not yet know everything that can be known.