Applied Mechanics and Graphic Statics
The angle of friction is:

The force of friction at which the body is just about to move
The angle between the normal reaction and the resultant of normal reaction and limiting friction
The force of friction when the body is in motion
The ratio of the friction and the normal reaction

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Applied Mechanics and Graphic Statics
When a body of mass M1 is hanging freely and another of mass M2 lying on a smooth inclined plane(α) are connected by a light index tensile string passing over a smooth pulley, the acceleration of the body of mass M1, will be given by

g(M2 × M1 sin α)/(M2 - M1­) m/sec²
g(M1 + M2 sin α)/(M1 + M2­) m/sec
g(M1 - M2 sin α)/(M1 + M2­) m/sec²
g(M2 + M1 sin α)/(M1 + M2­) m/sec²

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