I have two weights, weighing one ten times the other. I should figure out a way to make a pulley system that can lift the heavier mass with the smaller one. I would like to use the least number of pulleys possible because of the friction, but I think that anyway the rope would suffer from the same problem. I found this: http://science.howstuffworks.com/transport/engines-equipment/pulley.htm

But I cannot figure out how to continue. I would like to start from a system of 5\6 pulleys and make up a reasonable system. I believe that stress can be negligible.

Can anyone show how to go through such problems starting from adding pulley and decreasing the needed force, pulley by pulley, and then reduce the number of them adding sheaves or more complicated shapes? Thanks.

EDIT: Maybe adding some trusses among pulleys, can it be an advantage?


1 Answer 1


A good way to approach this problem is to first think about some of the characteristics of the system. A system of pulleys will need to reduce the force required to lift the larger mass by a factor of 10 (given the constraints of the problem), and thus the distance the smaller mass would need to pull to lift the mass a distance d would be 10d.

Then you can start building the system, adding pulleys one by one as necessary. As the HowStuffWorks article you linked showed, you need two pulleys to begin reducing the force needed to lift an object. To further reduce the force while keeping the number of pulleys to a minimum, you can re-wrap the rope around the two pulleys multiple times until you find that when the rope is pulled a distance x, the object will rise a distance of x/10.

I'm not quite sure about what you mean by adding trusses among pulleys, but I hope the rest of my answer helped.


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