The simple pulley enables the user to lift a load more easily by changing the direction from which the force is applied. When the rope is fixed at one end and another pulley is added, the system provides a mechanical advantage by multiplying the applied force, making it possible to lift heavy loads. More pulleys can be added to the system, now known as a "compound pulley" system, further multiplying the effectiveness of the force applied.
As an indication of the benefit of the system, the addition of a second pulley to a one-pulley lifting mechanism halves the amount of force required to make the lift. A third pulley, properly rigged, reduces the amount of force required to a quarter.
In 250 B.C.E., the Greek scientist and.-, .inventor Archimedes (c. 287-212 B.C.E.) adopted this principle by mounting several pulleys on the same axle to create a "block" that was much more convenient to use than a series of separate pulleys. A single rope—called the "tackle"—fixed at one end, can be threaded between a fixed block and around each of the pulleys ("sheaves") in a movable block so that the load on the system is shared between the ropes under tension.
According to Plutarch, whose account provides us with the earliest record of the block and tackle, Archimedes used his new invention single-handedly to move a whole warship. Whether this is true we cannot know, but the block and tackle has certainly been an essential tool for lifting and moving heavy loads ever since. It can be found today in the cranes and lifting gear used in construction, engineering, freight loading, and warehousing as well as on almost every yacht and sailing boat, including small dinghies with the simplest of rigging.
