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Simple pulley question- single fixed

  1. Jun 28, 2011 #1
    for a single fixed pulley system :

    1. on both sides -equal length ropes
    2. equal masses to balance each other (static)
    3. ignoring weight of the ropes and friction (pulley, rope, air etc..)

    ..if no friction- can it be assumed that the next incremental bit of weight on either side- (say a big fly lands on one side of the mass) will tip the scale so that one side completely pulls down the other
  2. jcsd
  3. Jun 29, 2011 #2

    Andrew Mason

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    You don't have to assume it. You can work it out. If the weights are not equal, there is a net force so there will be non-zero acceleration: F=(m1-m2)g = m1a. If there is non-zero acceleration, the distance that the system will move in time t is s = at^2/2 so one side will completely fall eventually.

    It should not be surprising that a fly would cause one side to fall. The real difficulty in practice would be to set up a frictionless pulley with equal masses on both sides so that they were exactly balanced.

    Last edited: Jun 29, 2011
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