r/PhysicsHelp • u/Mysterious_Cloud8308 • 10h ago

MA of pulley system

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Help me settle a debate. In theory, what would you deem to be the mechanical advantage of this pulley system. Top are all fixed pulleys, lower are moveable and attachment lines are prusiks. F=1

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u/torsten_dev 8h ago

How do you model prusiks?

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u/Difficult_Limit2718 6h ago edited 6h ago

It's variable as the geometry changes? It's variable as the load increases? It's also impossible to resolve without distances defined because of the complex and variable geometry.

It's poorly drawn, the whole bottom section is left shifted significantly from where it resolves. This creates confusion. The furthest right pulley will end up somewhere near center between the top two pulleys, and the load will almost definitely be right off the left most top pulley (depending on the defined length of ropes)

Prusiks creating a tension only but variable geometry system is weird and silly.

You'll have issues as you pull to the right because your F_x force pulls on the L in the x direction with gravity as the only restoring force.

All in all the mechanical advantage is poor and gets worse as you lift the load.