It is found that the relation between the surface friction f of cotton fabrics and the normal pressure R is generally well expressed by the following equation, when R is under 40g/cm2.
f=aRn where a and n are constants for the given surface of a fabric.
So it is difficult to explain fully the relation between f and R only with μ, the coefficient of friction.
Therefore the degree of slippage S is adopted.
when n=1, μ=1/S
For cotton fabrics, a>1, 1>n>0
The more the yarn is twisted and the denser the fabric is in the direction of slip, the larger S becomes.
