The angle between the resultant contact force and the normal force exerted by a body on the other is called the angle of friction. Show that, if λ be the angle of friction and μ the coefficient of static friction, 
Let us consider, the frictional force to be f,
The applied force= F
Normal reaction= R
Coefficient of friction force 
= 
When the force applied on the body increases, the force of friction also increases. It increases up to limiting friction 
.
Before reaching to the limiting friction
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