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Thread: Very Simple Pulley Question

  1. #1 Very Simple Pulley Question 
    Junior Member
    Join Date
    Aug 2013
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    2
    Please humor me on this very basic problem.

    Consider this scenario, involving a horse. A rider pulls on the reins, but the reins are redirected through a pulley system around the horse's neck (a martingale). What is the mechanical advantage, if any, provided by this set-up? In other words, if the rider pulls with 1 Newton of force on his end of the reins, what force is felt at the horse's end (via the bit on his mouth)? Feel free to ignore friction.

    I have drawn the basic underlying mechanics of this set-up, as well as provided an actual picture and a schematic. But this seems to me to be just a simple pulley, is it not?

    Thanks in advance.

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  2. #2  
    Senior Member
    Join Date
    Jan 2014
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    out there
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    There is zero mechanical advantage.

    To have mechanical advantage in a pulley system the load must be connected to a pulley or pulleys that move with the load (on the hook). The fixed pulleys on the ceiling do not contribute mechanical advantage, they simply redirect the force.

    Mechanical advantage in all pulley systems (and levers and gears) will only occur when the load moves less distance or rotates less than the source of the force or torque.
    In other words you pull two meters but the load move one meter. Or you rotate twice but the load rotates once. Think of a see saw. A child all the way at one end can lift an adult that is sitting a quarter length from the axle. The child moves up and down the full travel of the see saw but the adult only one quarter of that.
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