The equilibrium of systems with dry friction

The properties of the equilibrium positions of mechanical systems with Coulomb friction are discussed. A comparative analysis of various definitions of the concept of equilibrium is given. It is shown that the principles of virtual displacements and least constraint can be extended to the problem of statics with friction. The definitions of Lyapunov stability and Hill stability are examined; the latter approach has definite advantages in certain problems. Several mechanical examples are considered to illustrate the results obtained.