Friction is independent of the area of contact. The reason behind this is that the actual area of contact on an atomic scale is a fraction of the total surface area. Friction depends only on the nature of surfaces in contact and the weight of the body. If weight is different from the value of friction is also different.
- If the normal force is doubled, the area of atomic contact is also doubled and the friction becomes twice as large. But, if the geometric area is doubled whilst the normal force remains the same, the fraction of area in atomic contact is halved and the actual area in atomic contact hence the friction force remains constant.
- Friction force depends on the nature of the surface in contact.
- If the surface area is rough then the frictional coefficient of the surface will also be larger thus will need more force to slide increasing friction.
- If the surface area is smooth the co-efficient of friction between two surfaces will be less. Thus, friction depends on the nature of the surface in contact.