Nonrigid systems: mechanical and thermodynamic aspects

The motion of a uniform chain has been used to exemplify systems with variable mass. The discussion is usually confined to the dynamical aspects of the problem or to other derivations that use energy-conserving methods. Here this type of problem is re-examined by considering the chain as a closed one-dimensional motion, showing that the concept of centre of mass can be particularly useful in this kind of multi-particle system. It is similarly instructive to analyse the work-energy processes from the viewpoint of the first law of thermodynamics.