Differential pulley the system becomes a simple "gun tackle" with a mechanical advantage of 2. The same principle is used in a differential windlass, where the connected pulleys are replaced by winches. In the above graphic, the four segments of the chain are labelled W, X, Y and Z. The magnitudes of their corresponding forces are "F", "F", "F" and "F", respectively. Assuming that the chain is massless, "F" = 0 because segment X is not supporting any weight. Taking the system at equilibrium, "F" and "F" are equal — if they were not, the lower pulley would freely turn until they
Block and tackle output force), formula_5 is the ideal mechanical advantage of the system (which is the same as the number of segments of line extending from the moving block), and formula_6 is the mechanical efficiency of the system (equal to one for an ideal frictionless system; a fraction less than one for real-world systems with energy losses due to friction and other causes). If formula_7 is the number of sheaves in the purchase, and there is a roughly formula_8% loss of efficiency at each sheave due to friction, then: This approximation is more accurate for smaller values of formula_7 and formula_8. A