K4OJ's explanation is another way of saying energy is conserved. With
or without the pulleys the work is the same, e.g., 100 pound tower section
hauled 70 feet up is 7000 foot-pounds of work (energy.) If you use a 2:1
block and tackle, you'd pull 140 feet of rope but you'd exert only 50 pounds
of force on that rope. So 50 X 140 is still 7000 foot-pounds of work. All
this, BTW, ignores friction of the pulleys. And yes, I enjoy playing with
Gene Smar AD3F
From: Jim White <email@example.com>
To: jljarvis <firstname.lastname@example.org>; Chris BONDE <email@example.com>
Cc: firstname.lastname@example.org <email@example.com>
Date: Thursday, July 11, 2002 8:19 PM
Subject: Re: [Towertalk] mast disaster avoidance
>WHAT I FREQUENTLY DO IS USE THE GIN POLE NORMALLY AND THE WHEN THE ROPE
>DOWN TO GROUND LEVEL USE A SNATCH BLOCK SO A HORIZONTAL PULL IS NOW WHAT IS
>A SEPARATE BLOCK AND TACKLE ARRANGEMENT ANCHORED TO A TREE OR PICKUP TRUCK
>OR OTHER IMMOVABLE OBJECT ACTS AS ONE END (THE STATIC END OF THE BLOCK AND
>TACKLE....AND THE OTHER END - THE BLOCK THAT WILL BE MOVING IS ATTACHED TO
>THAT HORIZONTAL ROPE COMING DOWN FROM THE GIN POLE AND OUT THROUGH THE
>WHAT HAPPENS IS THAT THE LOAD IS DIVIDED OVER THE NUMBER OF TRIPS TO EACH
>AND FROM THE TWO PULLEYS IN THE BLOCK AND TACKLE ARRANGEMENT...
>SO HOW DOES THIS WORK - WELL YOU HAVE TO PULL A LOT MORE ROPE TO GET THE
>SAME NET AMOUNT OF MOVEMENT - THE SAME RELATIONSHIP EXISTS (INVERSELY) TO
>THE LENGTH OF ROPE PULLED AND AMOUNT OF ULTIMATE TRAVELED BY THE LOAD....
>EXAMPLE THE LOAD YOU ARE MOVING IS A SECTION OF 55g AT ABOUT 100 LBS
>IF YOU HAVE TWO ROPES BETWEEN THE BLOCK AND THE TACKLE PULLEYS YOU WILL
>LIKE IT IS A 50 POUND LOAD BUT YOU WILL HAVE TO PULL THAT FIFTY POUNDS TICE
>AS FAR - IF YOU LIFT THE TOWER SECTION ONE HUNDRED FEET YOU WILL PULL TWO
>HUNDRED FEET OF ROPE THROUGH THE BLOCK AND TACKLE....
>SAME LOAD BUT WITH 4X ROPES IN THE B&T....FEELS LIKE A 25 POUND LOAD BUT
>YOU HAVE TO PULL 400 FT OF LINE THROUGH THE BLOCK AND TACKLE TO MOVE THE
>LOAD 100 FEET....
>IT IS SIMILAR TO THE VOLTAGE CURRENT RELATIONSHIP IN ELECTRICAL POWER
>(COINCIDENCE, I THINK NOT) - YOU RUN THE 100 WATT APPLIANCE AT 100V AT 1
>OR 50V AT 2 AMPS OR 25 V AT 4 AMPS...
>NOTE THIS IS A LOT EASY TO PULL THIS WAY BUT TAKES COPIOUS AMOUNTS OF ROPE
>TO DO - WE FREQUENTLY WILL RE-SET THE BLOCK AND TACKLE SEVERAL TIMES TO
>AVOID HAVING IT AT THE OPPOSITE END OF THE PROPERTY FROM WHERE THE LOAD
>VERTICAL! PULL IT UP A THIRD OF THE WAY....RESET (OPEN UP THE BLOCK AND
>TACKLE SO THE TWO ARE FAR APART AGAIN...AND NOW ATTACH IT TO A LOOP TIED
>INTO THE LOAD ROPE AS IT EXITS THE SNATCH BLOCK
>SORRY FOR THE CAPS....TOO LAZY TO RETYPE IT...
>----- Original Message -----
>From: "Chris BONDE" <firstname.lastname@example.org>
>To: "jljarvis" <email@example.com>
>Sent: Thursday, July 11, 2002 6:20 PM
>Subject: Re: [Towertalk] mast disaster avoidance
>> It has been awhile since I have done any mechanical stuff with pulleys.
>> think that you are on the right road but not all the way.
>> If you are lifting a 100lb weight with one pulley at the top, you need
>> lbs on the other side to lift it. I would then say that there is 200+lbs
>> of weight on the pulley.
>> If you are lifting a 100lb weight with 2 pulleys at the top and one on
>> load, then you have a mechanical advantage and need only 1/3 of 100+ lbs
>> lift the weight (I think that that is correct, but it is a lot
>> less) Therefore, the total weight on the pulley is 100lbs plus the
>> amount hence less.
>> I think that this is correct.
>> Chris opr VE7HCB
>> At 02:00 PM 2002-07-11 -0400, jljarvis wrote:
>> >If you had a ginpole with a 2 wheel block on top (never seen
>> >one, myself. Do they exist?), you would reduce the load on each
>> >run of line, proportional to the number of lines.
>> >But the load on the axle is still the sum of the line-loads.
>> >i.e., unchanged.
>> >The compressive load on the ginpole itself is thus still the
>> >same, and the out-of-column bending loads are the same.
>> >From: "Mike Gilmer"<firstname.lastname@example.org>
>> >Date: Thu, 11 Jul 2002 12:16:03 -0300
>> >Subject: [Towertalk] Re: mast disaster avoidance
>> >I agree with most of N2EA's post except:
>> > > Solutions using added pulleys still leave the same load on
>> > > the ginpole material itself
>> >This is not true. As has been oft-discussed on this reflector in the
>> >past (and still misunderstood), judicious use of "added pulleys" can
>> >reduce the total load on the ginpole.
>> >Mike N2MG
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>> Self Supporting Towers, Wireless Weather Stations, see web site:
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>> any weather station price.
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>Self Supporting Towers, Wireless Weather Stations, see web site:
>Call 888-333-9041 to place your order, mention you saw this ad and take an
additional 5 percent off
>any weather station price.
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