# Simple pulley question- single fixed

1. Jun 28, 2011

### gloo

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. Jun 29, 2011

### Andrew Mason

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.

AM

Last edited: Jun 29, 2011