There is no friction unless the surfaces of the rubbed bodies have a structure that is in some way interfered with by the rubbing, while at the same time they offer a certain resistance to the disturbance. This resistance is due to a characteristic of matter, commonly called cohesion. Now we know that the inner coherence of a physical body is due to its point-relationship, that is to the gravitational force bound up with it. Indeed, cohesion increases as we pass from the gaseous, through the liquid, to the solid state of matter.