Pulleys
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Fixed pulley
A pulley is a simple machine made of a grooved wheel with a rope or cable wrapped around it. You use a pulley by pulling on one end of the rope. This is the input force. At the other end of the rope, the output force pulls up on the object you want to move. To move a heavy object over a distance, a pulley can make work easier in two ways. First, it can decrease the amount of input force needed to lift the object. Second, the pulley can change the direction of your input force. For example, you pull down on the flagpole rope, and the flag moves up.
Types of Pulleys
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There are two basic types of pulleys. A pulley that you attach to a structure is called a fixed pulley. Fixed pulleys are used at the top of flagpoles. If you attach a pulley to the object you wish to move, you use a movable pulley. By combining fixed and movable pulleys, you can make a pulley system called a block and tackle. The ideal mechanical advantage of a pulley is equal to the number of sections of rope that support the object.