Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Pulleys: How do they exactly work?

  1. Apr 13, 2007 #1
    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. jcsd
  3. Apr 13, 2007 #2


    User Avatar
    Gold Member

    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]
  4. Apr 13, 2007 #3
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook