A type of simple machine consisting or a rope and grooved wheel, the pulley is used in a number of machines and basic applications today. Although no one really knows when the first pulley was invented, pulleys were used in the medieval period and may date back to ancient times.
Dumb Waiters and Elevators
Both elevators and dumb waiters use pulley systems created to lift weight. A smaller version of the elevator, a dumb waiter typically consists of both fixed and movable pulleys, a motor, some cable and a counterweight. The counterweight uses gravity to reduce the amount of weight the motor must pull. An elevator works on the same principle as the dumb waiter; however, most elevator counterweights are equal to the weight of the elevator itself plus 40 per cent of the elevator's maximum weight limit.
If you've ever stood in line at the supermarket checkout line, you've seen pulleys in action. The conveyor belt that moves your groceries along consists of a belt with two pulleys at either end. Both pulleys move as the belt moves to convey your groceries to where they're supposed to go. You'll also find conveyor belts in factories and other manufacturing businesses. The conveyor belt is an example of a movable pulley system.
When you try to close or open your window blinds, you're using a pulley. The cord you pull on to move your blinds up or down is attached to a fixed pulley or two at the top. Each time you pull the cord on your blinds to raise them, the pulley allows you to pull the string which controls the blinds with little effort. If your blinds ever refuse to go up or down, there's a good chance one or both of the pulleys used in the blind construction are broken.
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