Abstract
Once the concept of work has been introduced, the concepts of reversibility, equilibrium, and entropy become clearer and can be better defined. This was the task undertaken by classical mechanics.
Keywords: Quasi-static process, Reversibility, Frictionless process, Local equilibrium, Maximum work, Overall increase of entropy, Irreversible process, Cyclical process, Carnot cycle, Maximum theoretical efficiency, Work accumulation, Engines, Real process, Particle motions, Balancing of forces, Energy levelling, Maximum entropy, Equilibrium, Stable state.