A pulley allows you to use less force to perform the same amount of work by changing the direction of the force you apply, and it can also provide a mechanical advantage when used in combinations (like a block and tackle system).
Here's how it works:
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Mechanical Advantage: When you use multiple pulleys in a system (like a block and tackle), you can distribute the weight of the load across multiple ropes. This reduces the amount of force you need to exert to lift the load. For example, if you have a system with two pulleys and you pull down on the rope, the load effectively feels only half the weight because the force is spread across two segments of rope.
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Force Direction Change: A single fixed pulley doesn't change the magnitude of the force required, but it allows you to pull down on the rope to lift an object upward. This can often make it easier to lift heavy objects since pulling down is generally more comfortable and easier than lifting up.
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Work Conservation: The principle of work states that work (force times distance) remains constant in an ideal system with no friction. With a pulley system, while you may exert less force over a longer distance to lift the same weight, the total work done remains the same. For example, if a load is lifted 1 meter by someone pulling down 100 Newtons, they do 100 joules of work. In a pulley system where you only pull with 50 Newtons, you would need to pull the rope for 2 meters to do the same amount of work (50 N x 2 m = 100 joules).
In summary, pulleys allow you to exert less force by creating mechanical advantages and making it easier to lift loads by changing the direction of the applied force.