This is a hash of my high school physics teacher's illustration on pulley
mechanics. Stuck with me ever since. Something about a picture worth a 1000
Lightweight Larry weighs 100 pounds. Normal Nelson weighs 150. Heavy Henry
weighs 300 pounds. The tower section weighs 300 pounds.
Straight pulley: Heavy Henry on one side holding steady, section on the other.
600 pounds on the top hook.
2:1 advantage: Normal Nelson on one side holding steady, section on the other.
450 pounds on the top hook.
3:1 advantage: Lightweight Larry on one side holding steady, section on the
other. 400 pounds on the top hook.
Fun part was class asked to calculate acceleration of Lightweight Larry on the
> From: David Robbins <firstname.lastname@example.org>
> Date: 2001/06/13 Wed PM 02:21:59 EDT
> To: K7LXC@aol.com, reflector -tower <email@example.com>
> Subject: Re: [TowerTalk] Ginpole for 20 foot sections
> of course the lifting rope load remains the same, but the force required on
> 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
> have a 300lb load plus 300lb of pull from the other side giving you a worst
> 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
> 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
> the same distance.
> K7LXC@aol.com wrote:
> > 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
> > of
> > > 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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