The concepts of work and heat and the first and second laws of thermodynamics

Abstract

A simple and effective approach to thermodynamics is suggested, which solves the major difficulties in the traditional presentation of the subject. The internal energy is introduced from the behavior of deformable bodies, whereas the importance of keeping in mind the microscopic picture is emphasized. A straightforward model is used to show that the internal energy depends on the volume and entropy, from where the relationship between mechanics and thermodynamics is immediate, mechanics corresponding to isentropic thermodynamics. The questions of evolution to equilibrium and irreversibility are studied under the light of the action of the "dynamic force", which has a dissipative character. The present formulation leads to a discussion and clarification of the physical meaning of various thermodynamic quantities, such as pressure, temperature, work and heat. The adiabatic piston problem is analyzed, as a paradigmatic case where the notions of "adiabatic" and "heat transfer" are often ill-defined.