Nothing "magical" about it...
http://www.howstuffworks.com/pulley.htm
has some good graphics although no description of the force on the fixed pulley
(our ginpole), so one needs to sum up all the "down" forces.
73 Mike N2MG
On Wed, 13 June 2001, n4kg@juno.com wrote:
>
> The pulley at the top of a gin pole merely changes
> the direction of the rope. Please explain how a
> block and tackle "Magically" reduces the force on
> the rope to the top pulley and how to install the
> block and tackle to achieve this magical reduction.
>
> One more point. One pulley can give a 2:1 mechanical
> advantage if one end of the rope is attached to a FIXED
> support. If both ends of the rope are moving, there is
> NO mechanical advantage, only a direction change
> plus loss due to friction.
>
> de Tom N4KG
>
> On 13 Jun 2001 Mike Gilmer - N2MG <n2mg@contesting.com> writes:
> > Steve, you are "half" right.
> >
> > The lift effort is part of the overall load on the
> > ginpole (everyone forgets this), so without any
> > mechanical advantage there is 2X load weight applied
> > to the ginpole. If you employ a 3:1 advantage, and
> > thereby reduce the lift force needed, you decrease the
> > overall force on the ginpole.
> >
> > 73 Mike N2MG
> >
> > On Wed, 13 June 2001, K7LXC@aol.com wrote:
> >
> > > In a message dated 6/12/01 11:45:50 PM Pacific Daylight Time,
> > > w7ni@easystreet.com 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.
> > >
> > > Cheers, Steve K7LXC
> > > Tower Tech
> >
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