Friction force is partly caused by adhesive contacts. These contacts depend on the type of material, surface finish of the mating surfaces, and many other factors. To determine the coefficient of friction between two objects A and B for example,. One of the objects is placed over a mobile platform, and the other is placed over the first object as shown. A thread to a force transducer stretches the object on the top. The platform is pulled by a constant speed. The force indicated by the force cell is noted.

A load is placed over the object and the procedure is repeated several times. A graph is plotted such as the friction force against the normal force,. µ = F t /F n Eq µ = tan αEq. 12.2

Another method to determine the coefficient of friction is to place object A over object B. Object B is fixed to an adjustable tilting table. The table is then gradually tilted till object A is just begin to slide over object B. At this instant the tilting angle is noted. The tangent of the tilting angle is equal to the coefficient of friction. Mg sin α = µ mg cosα Eq µ = tan αEq. 12.4