Friction Force in a Lifting Machine:
The effort required to lift the load W is P. In an ideal lifting machine MA = VR.
or, Ideal load / P = VR
or, Ideal load lifted = P × VR
Thus, Friction force (F) = Ideal Load lifted - Actual load lifted
F = P × VR - W
The above expression determines friction force in terms of load lifted. The friction force in terms of effort applied shall be expressed as :
FP = F /VR
= P - (W /VR)