polie

Pulley comes from Old French polie, from Medieval Latin *polidia, probably from Greek polos (axis, pivot). A pulley is a grooved wheel over which a rope or cable runs, redirecting the direction of force. Pull down on one end of the rope, and the load on the other end goes up. The principle is so simple that Archimedes reportedly claimed he could move a ship with a system of pulleys — and then demonstrated it for King Hieron II of Syracuse.

The compound pulley — multiple wheels working together — multiplies force. A two-pulley system halves the force needed to lift a load (at the cost of pulling twice the length of rope). Medieval construction used compound pulleys to raise the stones of cathedrals. The Gothic cathedral is impossible without the pulley: no human can lift a cut stone block to the height of a nave. Pulleys made vertical ambition achievable.

The Industrial Revolution mechanized the pulley. Factory systems used belt-and-pulley arrangements to distribute power from a central steam engine to individual machines. Long shafts ran along ceilings, connected by belts to pulleys on each machine below. The factory floor was a forest of spinning pulleys. This system was standard from the 1780s until electric motors replaced it in the early twentieth century.

Modern pulleys are everywhere and largely invisible. Elevator systems use pulleys. Window blinds use pulleys. Garage doors use pulleys. Cranes, sailboats, rock-climbing systems, and gym equipment all use pulleys. The technology is five thousand years old and has not been improved upon — only refined.