The sliding friction coefficient — its evolution and usefulness

Braithwaite (1978) expressed the opinion that the term coefficient of friction has served its usefulness and will eventually be of historical interest only.

After recalling the historical period (16th–18th centuries), this survey covers the period of more modern (simple and mixed) theories (18th–20th centuries); the energy problem is discussed separately. Then, the use of the friction coefficient is examined in thermal processes, vacuum, radiation, thin layers, solid lubricants, plastic and ceramic materials, and the friction-wear dependence, stick-slip motion and various lubrication regimes (from boundary to elastohydrodynamic lubrication) are considered.

The conclusion that is reached is that, instead of becoming a notion of historical interest only, the friction coefficient has been increasingly improved, adapted and employed, becoming at least a “tool” even in the new theories. It can hardly be avoided in the evaluation of friction effects.