Although a larger area of contact between two surfaces
would create a larger source of frictional forces, it
also reduces the pressure between the two surfaces for
a given force holding them together. Since pressure
equals force divided by the area of contact, it
works out that the increase in friction generating area
is exactly offset by the reduction in pressure; the
resulting frictional forces, then, are dependent only on
the frictional coefficient of the materials and the
FORCE holding them together.
If you were to increase the force as you increased the
area to keep PRESSURE the same, then increasing the
area WOULD increase the frictional force between the
Answered by: Paul Walorski, B.A. Physics, Part-time Physics Instructor
'Wisdom is the daughter of Experience, Truth is only the daughter of Time.'