**ZN/P ****curve** - general graphic representation of the equation: µ = (f) ZN/P, where µ (the *coefficient of fr**iction *in a *journal *bearing) is a function (f) of the dimensionless parameter ZN/P, (viscosity x speed) / pressure. This is the fundamental lubrication equation, in which the coefficient of friction is the friction per unit load, Z the viscosity of the lubricating oil, *N *the rpm of the journal, and *P *the pressure (load per unit area) on the *bearing. *The ZN/P curve illustrates the effects of the three variables *(viscosity, *speed, and load) on friction and, hence, on lubrication. See *boundary lubrication*, *full**-flu**id-film* *lubri**c**ation.*