<P> Diagram 3a: The Luff tackle adds a fixed pulley "rove to disadvantage ." The tension in the rope remains W / 3 yielding an advantage of three . </P> <P> The mechanical advantage of the gun tackle can be increased by interchanging the fixed and moving blocks so the rope is attached to the moving block and the rope is pulled in the direction of the lifted load . In this case the block and tackle is said to be "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 . </P> <P> 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 . </P> <P> 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 system, the massless and frictionless pulleys do not dissipate energy and allow for a change of direction of a rope that does not stretch or wear . In this case, a force balance on a free body that includes the load, W, and n supporting sections of a rope with tension T, yields: </P>

What is an example of a compound pulley