Pulleys: How do they exactly work?

[DrHughes]

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?

 

[Mentz114]

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.

$$F_1 = F_2\frac{D_2}{D_1}$$

 

[e(ho0n3]

See these links:

http://www.howstuffworks.com/pulley.htm
http://www.batesville.k12.in.us/physics/phynet/mechanics/Energy/Labs/pulley_lab_1.htm