ABSTRACT
When two bodies are placed in contact, the actual microscopic area of the contact is much less than the apparent macroscopic area of the contact. The actual area of the contact is proportional to the normal force because the contact points deform plastically under heavy stress developed at these points. These contact points become ‘cold-welded2*5 and produce ‘surface adhesion5. At the contact points, the molecules on the opposite sides of the surface are so close to each other that they exert strong intermolecular forces among the molecules. When one body is pulled across another, the frictional resistance is associated with the rupturing of these thousands of tiny welds that continually reform as new contacts
are made, as seen in Figure 2. It would be appropriate to divide the studies related to the friction into the following two groups:
• Friction of hard solids. • Friction of fibrous and viscoelastic materials.
