Pulley Systems in Everyday Life

Blinds

• Window blinds are probably the most common pulley system in the average home. You pull on the cord and the pulley redirects the downward motion you are supplying into the upward motion needed to raise the blinds. Gravity does the job of lowering the blinds when that is required. Some blinds will have a second pulley system that is somewhat unusual --- this pulley has a mechanism attached to its axle that causes the slats of the blinds to open and close. The purpose of this pulley is not redirecting the force of the pulled rope but to use this force to operate another mechanism.

Pulleys on Poles

• On the top of most large flagpoles there is a pulley. The person at the bottom pulls a rope --- which is usually a big loop --- to raise a flag. When the flag is in place, the rope is tied around a cleat near the bottom of the pole to keep the flag in place. There is a similar arrangement at the top of the mast of a sailboat to raise the sail and hold it in place. Such ropes on a sailboat are called "halyards." There is also a pulley on top of the "gin poles" used on construction sites and by circuses to raise the tents for the big top.

Elevators

• Elevators are the most common of several pulley systems that have a weight on each end of the rope or cable that goes over a pulley. This makes it easy to position the system wherever you want it to be. Dumb waiters use a similar arrangement. In the walls of some old houses, there is a similar system where one end of the rope is attached to a window and the other end of the rope is attached to a weight. This makes it easy to position the window where you want it to be.

Block and Tackle

• A block is a row of pulleys --- usually two or three --- that share a common axle. These blocks are used in pairs. One is firmly attached to a frame and the other is attached to the load to be lifted. A single rope runs back and forth between the blocks --- going over a different pulley in the block each time. When the free end of the rope is pulled, the load --- with one of the blocks --- moves toward the fixed block. This multiplies the lifting force by the number of individual pulleys.