Thermodynamics of Friction

Everything goes around in construction-deconstruction-construction...

In the previous post we considered viscosity in laminar and turbulent flow and friction between solid bodies as mechanisms for irreversible transformation of large scale kinetic motion/energy into small scale kinetic motion/energy in the form of heat energy, noting that the transformation cannot be reversed since the required very high precision cannot be realised, everything captured in a 2nd Law of Thermodynamics.  

Let us consider the generation of heat energy in friction when rubbing your hands or sliding an object over a floor or pulling the handbrakes of your bicycle. We understand that the heat energy is created from the work done by force times displacement (in the direction of the force), like pressing/pushing a sandpaper over the surface of a piece of wood to smoothen the surface by destroying its granular micro-structure. Work is thus done to destroy more or less ordered micro-structure and the work shows up as internal heat energy as unordered micro-scale kinetic energy. 

The key is here destruction of micro-structure into heat energy in a process which cannot be reversed since the required precision cannot me met.

Skin friction between a fluid and solid acts like friction between solids. 

Turbulent flow transforms large scale ordered kinetic energy into small-scale unordered kinetic energy as heat energy under the action of viscous forces. Laminar flow also generates heat energy from friction between layers of fluid of different velocity.

In all these cases heat energy is generated from destruction/mixing of order/structure in exothermic irreversible processes. This destruction is balanced by constructive processes like synchronisation of atomic oscillations into radiation and emergence of ordered structures like vortices in fluid flow and endothermic processes of unmixing/separation. 

We thus see exothermic processes of destruction followed by endothermic construction, which is not reversed deconstruction, with different time scales where deconstruction is fast and brutal without precision and construction is slow with precision. This is elaborated in The Clock and the Arrow in popular form. Take a look.