Why does the frictional force decrease with the increase of angle of inclination?
The frictional force is calculated by the normal force * the coefficient of friction.
The normal force is mg*cos(angle).
When the angle is 0, the normal force is mg.
However, as the angle increases, cos(angle) decreases and so mg*cos(angle) decreases.
So the normal force decreases as the angle of inclination increases.
It follows that the frictional force decreases since the frictional force is the normal force * the coefficient of friction.
