Consider a mass m lying on an inclined plane, If the direction of motion of the mass is down the plane, then the frictional force F will act up the plane. This can be seen in the image below.

N = normal force exerted on the body by the plane due to the force of gravity i.e. mg cos θ
f = frictional force
mg = mass x gravity

The weight of the mass is mg and this will cause another 2 forces to act on itself, these being N and mg sin θ.
Forces up the plane = Forces down the plane
(f = mg sin θ)
Forces up = forces down
(N = mg cos θ)
If we divide the 2 equations above we get:
But therefore tan θ = µ
µ = The coefficient of friction
By gradually increasing θ until the mass begins motion then value of θ will be called the limiting angle of repose, with this you can obtain the maximum value of µ for static friction.
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