Pulley If there are "p" of these parts of the rope supporting the load "W," then a force balance on the moving block shows that the tension in each of the parts of the rope must be "W/p." This means the input force on the rope is "T"="W/p." Thus, the block and tackle reduces the input force by the factor "p." The simplest theory of operation for a pulley system assumes that the pulleys and lines are weightless, and that there is no energy loss due to friction. It is also assumed that the lines do not stretch. In equilibrium, the
Fly system used for spot rigging, where they are often equipped with swivel-pivots to divert lines across a large range of angles. Tension blocks are single-sheave blocks located at the lower end of the arbor guide track, beneath the arbor. The operating line is reeved through the tension block from the bottom of the arbor through the rope lock. Tension blocks typically ride vertically along the arbor guide system tracks, instead of being fixed, to allow for variation in the length of the operating line. Counterweights are heavy objects that are used to balance the lineset loads in a fly system. In