Global and local coefficients of friction and explanation of their dependence on pressure
The coefficient of friction - one of the main characteristics of friction is not blameless. Any ratio is the ratio between the values. If the value that is in the denominator can be zero then this ratio in the neighborhood severely degraded, leaving the physical sense. The intense increase in the coefficient of friction with decreasing normal pressure due to the presence of constant component in the friction force is independent of the pressure. The main part of this component is the adhesion or molecular interaction surfaces. Because of this constant component division friction on value close to zero leads to a sharp increase in the friction coefficient.