of course the lifting rope load remains the same, but the force required on the
pulling end decreases so the total load on the gin pole does get reduced.
for example, with a standard gin pole lifting 300lbs at the top of the pole you
have a 300lb load plus 300lb of pull from the other side giving you a worst case
600lb force on the gin pole (static load, some more is required to get things
moving, overcome friction, etc).
with a 3:1 advantage pulley system you still have the 300lb load on one side,
but the rope pulling down on the other side is only adding 100lbs of force to
the pole, so the total is now 400lb. which of course is a 1/3 reduction from
the 600lb you started with.... note the 3:1 and the 1/3 reduction is just how it
works out. with a 2:1 advantage you only reduce the total load from 600 to
450lbs of a reduction of only 1/4 of the load... and taken to extreme, with an
infinite mechanical advantage you still have 300lbs of load so you only reduce
the total load on the pole by 1/2, the lowest you can get.
another advantage of a pulley system like that is you can use a lighter weight
rope since each pass of it between the pulleys divides the load up. so for a
3:1 system with a 300lb load you only need a rope that can handle 100lb of
tension instead of 300lb... but of course you have to pull 3x more of it to lift
the same distance.
> In a message dated 6/12/01 11:45:50 PM Pacific Daylight Time,
> firstname.lastname@example.org writes:
> > A 3:1 mechanical advantage block and tackle system does, indeed, relieve
> > about 1/3 of the load on the gin pole, in addition to reducing the number
> > bodies required on the pull rope.
> You sure? Isn't a hundred-pound load going to weigh 100 pounds no matter
> how the block and tackle are set up? The load effort on the end of the rope
> will be reduced but the dead weight of the load stays the same. You still
> need a suitable ginpole.
David Robbins K1TTT
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