@$#%!!!!

Studying counterweight scenery system. And I'm not happy about it. All of these diagrams from my prof have two pullies to demonstrate mechanical advantage, but I can't figure out how those work, since one end of the purchaseline/drift is fixed and that seems to not let anything move. And if neither end is fixed, and you have, for example, three pullies, how does the 25 lb arbor balance with the 75 lb flat? I understand that you can move the 75 lbs by just moving the 25lbs, but unless it's clamped in place somehow, shouldn't the flat fall? How would it be clamped? Oh, I am so confused...

Luckily, all I have to do is label a diagram, and that I can do. Who says I actually have to know how this crap works? I'm gonna be teaching junior/senior high Drama. What little scenery I have will be made out of old refrigerator boxes.