Independence of friction and area of contact

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Friction does not depend on the area of contact because the coefficients of friction remain constant regardless of the contact area. The total friction force is influenced by the normal force and the average pressure on the surfaces in contact. When two surfaces are pressed together, the local tangential force is proportional to the pressure acting on them. This relationship leads to the conclusion that total friction can be expressed as a function of the normal force, independent of the contact area. Thus, while total friction is affected by area, the coefficient of friction itself is not.
prasanna
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Can anyone tell me why friction does not depend on the area of contact??
 
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Total Friction does depend on the area of contact. The coefficients of friction do not.
 
The short version is:
If two surfaces is pushed "hard" together they will tend to stick, and the local tangential force will typically be proportional to the PRESSURE acting locally.
The average pressure on the surface ought clearly be N/A, where N is the normal force, whereas A is the contact area.
The LOCAL tangential force (acting on a surface element "dA") can therefore, on average equal to kN/A*(dA), where k is a dimensionless constant.

Summing up the local frictions, gives us the total friction as:
F=k*(N/A)*A=kN
 
Thanks arildno!
 

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