Pulleys: How do they exactly work?

In summary, using multiple pulleys reduces the amount of force needed to lift an object because it distributes the force over a longer distance, similar to using a lever. This is due to the work being the same at both ends, resulting in the forces varying inversely with the distance. For more information on how pulleys work, you can refer to the provided links.
  • #1
DrHughes
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Having multiple pulleys reduce the amount of force you have to exert to pull up an object?

why is that exactly?

I mean, I use this principle whenever I encounter a pulley Q...w/o really understanding why that's the case...

Can someone expain in terms of Newtoniam mechanics and/or Free BOdy diagram?
 
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  • #2
It's a question of leverage. When you use a lever, the distance you move the one end is greater than the distance moved at the other. This distributes the force needed to do work over a longer distance. A pulley system does the same. The mechanics is straightforward because, assuming no friction, the work done ( force times distance) is the same at both ends. If the work is the same, then the forces vary inversely with the distance.

[tex] F_1 = F_2\frac{D_2}{D_1} [/tex]
 

1. How does a pulley system work?

A pulley is a simple machine that uses a wheel with a groove or groove-like notch along its edge and a rope or belt around the wheel to change the direction of a force. When a force is applied to one end of the rope, the pulley redirects the force in a different direction, allowing heavy objects to be lifted with less effort.

2. What are the different types of pulleys?

There are three main types of pulleys: fixed, movable, and compound. A fixed pulley has its wheel attached to a fixed point, such as a ceiling or wall, and only changes the direction of the force. A movable pulley has its wheel attached to the object being lifted and reduces the amount of force needed to lift the object. A compound pulley combines multiple fixed and movable pulleys to further decrease the amount of force needed to lift an object.

3. How do I determine the mechanical advantage of a pulley system?

The mechanical advantage of a pulley system is determined by counting the number of ropes supporting the object being lifted. For example, a single fixed pulley has a mechanical advantage of 1, as it only changes the direction of the force. A movable pulley or compound pulley has a mechanical advantage equal to the number of ropes supporting the object, so a movable pulley with two ropes has a mechanical advantage of 2.

4. What are some real-life examples of pulleys?

Pulleys are used in a variety of everyday objects, such as flagpoles, elevators, cranes, and even exercise machines like weightlifting equipment. They are also commonly used in sailing and rock climbing to hoist heavy objects or to support the weight of a person.

5. Are there any disadvantages to using pulleys?

While pulleys can greatly reduce the amount of force needed to lift heavy objects, they also introduce some friction into the system, which can decrease efficiency. Additionally, if the rope or belt is not strong enough, it can break under heavy loads, causing the object being lifted to fall. It is important to carefully consider the strength and quality of the materials used in a pulley system to ensure safe and efficient operation.

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