1.Introduction-If power transmitted between two shafts is small, motion between them may be obtained by using two plain cylinders or discs 1 and 2 as shown in fig.-If there is no slip of one surface relative to the other, a definite motion of 1 can be transmitted to 2 and vice-versa. Such wheels are termed as “friction wheels”. However, as the power transmitted increases, slip occurs between the discs and the motion no longer remains definite.-Assuming no slipping of the two surfaces, the fo