Movement No. 18 presents a classic and historically significant pulley configuration: a combination of two fixed pulleys and one movable pulley — one of the most practical and widely recognized forms of the block-and-tackle system. In this arrangement, the two fixed pulleys are mounted overhead on a stationary support structure and serve purely as direction-change devices, redirecting the path of the rope without contributing to mechanical advantage themselves. The single movable pulley is attached directly to the load, and it is this movable pulley that provides the mechanical advantage of the system. A single continuous rope threads through all three pulleys — starting from a fixed attachment point, passing under the movable load pulley, then over one or both of the fixed upper pulleys, and finally reaching the operator’s hand as the free effort end. The load is effectively supported by two rope segments, meaning the mechanical advantage is 2: the operator needs to apply only half the force of the load’s weight to lift it, at the cost of pulling the rope twice the distance of the load’s rise. The two fixed upper pulleys allow the operator to stand clear of the load and apply force in a convenient direction — typically downward — making this a highly practical arrangement for real-world lifting tasks. This mechanism has been used for centuries in shipboard rigging, building construction, theater stage machinery, and workshops, and remains a fundamental teaching example in classical mechanics and engineering education.
18. Is a combination of two fixed pulleys and one movable pulley.