Strength and pulleys

Question

How does it work metal wires, and pulleys?

Had a quick chat with a crane operator, using a wire for lifting. Asked what the max load he could lift. He said X amount, but if he uses a pulley, he could lift almost 2 times X.

Is this true? Is there a max to how many pulleys you can use/weight you can lift
Is the lifting curve linear or exponential?

TYIA

In: 20

Answer 1

you can lift more, but over a shorter distance (you need more wire/rope), because you’re essentially doubling up the wire, so for each pulley you can pull (nearly) twice as much as before, i.e. you’re using 2 wires, each with its own capacity. Think of a pulley as a “cut” of the wire and then each wire that hangs down from the pulley as its own wire – then it makes more sense intuitively that it doubles the capacity.

Each pulley slightly decreases the total capacity because the wire is bending, but not by much, so if you have a long enough wire and a supporting structure that can handle it, you can get quite a few pulleys in there, but that’s more academic – for real situations, I’ve seen 6 or 7 pulley block and tackles. There’s probably bigger ones.

Answer 2

you can lift more, but over a shorter distance (you need more wire/rope), because you’re essentially doubling up the wire, so for each pulley you can pull (nearly) twice as much as before, i.e. you’re using 2 wires, each with its own capacity. Think of a pulley as a “cut” of the wire and then each wire that hangs down from the pulley as its own wire – then it makes more sense intuitively that it doubles the capacity.

Each pulley slightly decreases the total capacity because the wire is bending, but not by much, so if you have a long enough wire and a supporting structure that can handle it, you can get quite a few pulleys in there, but that’s more academic – for real situations, I’ve seen 6 or 7 pulley block and tackles. There’s probably bigger ones.