A pulley can be used to provide mechanical advantage while lifting weight. Suppose a combination pulley is made such that in order to lift something four times heavier, one can use the same force but the rope needs to be pulled four times further. The rope needs to be pulled further in order to conserve energy.

But i was just curious if there is any system or arrangement which will follow the law of conservation of energy by which one could reduce the effort used to lift the load and on top of that will not have to pull the rope further.

  • 2
    $\begingroup$ I think that is what everybody is after when they are chasing for an implementation of free energy. $\endgroup$
    – NMech
    Sep 13, 2020 at 16:12
  • $\begingroup$ Work has the units of kg m^2/sec^2. This can be decomposed into force - Kg m/sec^2 - times distance - m. So no - force times distance is what work (energy change) is. 1/4 the force needs 4 times the pull distance to conserve energy. $\endgroup$
    – Phil Sweet
    Sep 13, 2020 at 21:06

1 Answer 1


If you use a counterweight like elevators do, the only energy you have to invest is that what is needed to overcome the mechanical friction plus what is needed to lift the elevators load. Ofcourse you would have to invest additional energy for the first use to get the counterweights up there and it obviously only works if whatever you lift you will drop again to use its mass to lift the counterweights up again.

  • $\begingroup$ This slows down acceleration though. Not a problem though if you dont want a fast system. Likewise you can store e ergy in springs or a hydraulic/pneumatic system $\endgroup$
    – joojaa
    Sep 15, 2020 at 4:45

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