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Part 1: Pulleys

Part 1: Pulleys. What is a pulley?. Pulleys may have been invented by Archimedes in ancient Sicily, about 250 BC . A pulley consists of a rope (or a belt or a chain) that passes around a wheel. Sometimes the pulley is fixed, and sometimes it moves with the object that is

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Part 1: Pulleys

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  1. Part 1: Pulleys

  2. What is a pulley? Pulleys may have been invented by Archimedes in ancient Sicily, about 250 BC. A pulley consists of a rope (or a belt or a chain) that passes around a wheel. Sometimes the pulley is fixed, and sometimes it moves with the object that is being shifted. As with a screw, you can use a pulley in several different ways. You can use a pulley to make it easier to pull a rope, to change the direction of a force, or to get more mechanical advantage and lift something heavier than you can lift by yourself. With a fixed pulley, the pulley is attached to a hook or a wall and doesn't move, like the clothesline pulley in the picture here. A fixed pulley doesn't give you any mechanical advantage, but it changes the direction of the force. For instance, you can pull down in order to lift something up, or you can pull the upper clothesline toward you in order to move the lower clothesline away from you. With a movable pulley, you do have a mechanical advantage: you can pull with less force for a longer distance to get the same work done. This lets you lift things that would be too heavy for you without a pulley.

  3. Part 2: Moving pulleys

  4. What is a moving pulley Diagram 10 shows one moving pulley attached to the engine (the load), and one fixed pulley attached to the support above. This type of pulley system is called a 'block and tackle', where 'block' refers to the pulleys and 'tackle' is the chain that the person is pulling to lift the engine. The fixed pulley changes the direction of the force to make it more convenient. This means that the person can lift the load by pulling down on the rope. The moving pulley gives a mechanical advantage and makes it easier to lift the load. In a pulley system, each moving pulley halves the effort, but means that the effort has to be applied for twice the distance. This is why a person can lift an engine out of a car using only a 'block and tackle'. The mechanical advantage is achieved by pulling the chain over a much longer distance than the distance that the engine is actually lifted.

  5. The End

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