Differential pulley were. Next, the downward force acting on the lower pulley equal the upward forces acting on it, so Additionally, there is no net torque or moment around the compound pulley, so the clockwise torque is equal to the anticlockwise torque: Substituting "F" and "F" from the above equations, Rearranging gives As "F" = , Finally, the mechanical advantage, = or . Differential pulley A differential pulley, also called "Weston differential pulley", sometimes "chain hoist" or colloquially "chain fall", is used to manually lift very heavy objects like car engines. It is operated by pulling upon the slack section of a
Block and tackle blocks. Frictional losses also mean there is a practical point at which the benefit of adding a further sheave is offset by the incremental increase in friction which would require additional force to be applied in order to lift the load. Too much friction may result in the tackle not allowing the load to be released easily, or by the reduction in force needed to move the load being judged insufficient because undue friction has to be overcome as well. A block which is open or can be opened to engage with a bight, without the necessity to thread the