Pulley "rove to advantage." Diagram 3 shows that now three rope parts support the load "W" which means the tension in the rope is "W/3". Thus, the mechanical advantage is three. By adding a pulley to the fixed block of a gun tackle the direction of the pulling force is reversed though the mechanical advantage remains the same, Diagram 3a. This is an example of the Luff tackle. The mechanical advantage of a pulley system can be analyzed using free body diagrams which balance the tension force in the rope with the force of gravity on the load. In an ideal
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