Stopping objects with zero external work: Mechanics meets thermodynamics

Abstract

Although the work-energy theorem of pure, nondissipative mechanics states that the work done stopping a body equals its kinetic energy change, the work done stopping a body via an inelastic, dissipative collision can be zero. This counter-intuitive result is used to motivate the development of thermodynamic ideas as a direct extension of classical mechanics. The approach leads to a natural introduction of internal energy, the path dependence of work, and dissipation. It also offers an opportunity for early exposure to powerful symmetry and frame-invariance arguments. The main presentation addresses one-dimensional highly symmetric collisions, with a generalization in the Appendix.