# Pulleys: How do they exactly work?

1. Apr 13, 2007

### 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?

2. Apr 13, 2007

### 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.

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

3. Apr 13, 2007