posted on Sep, 9 2008 @ 06:01 PM
dave420 is correct, basically. If you are lifting a mass of 9100 kg (20 000 lbm), and you use three movable pulleys (the pulleys at the bottom), then
the force you must apply at the free end of the cable is 14.83 kN, which is far more than a human weighs. But what almost everyone on almost every web
site seems to not understand about physics is that you do not merely hang a weight (your own body weight) to the free end of the cable, in that case.
You instead attach the free cable end to a hand-operated winch (sometimes called a "come along"), then anchor the winch to a fixed point, such as
the bottom of one of those massive telephone poles used by Leedskalnin. He often used a manual winch, but most sites give misinformation and
erroneously fail to mention this.
And, if the manual winch does not apply enough tensile force to the free cable end, then you can use even more physics (mechanical advantage,
leverage) to increase the applied cable tension further. All you need to do is anchor the free cable end directly to a fixed anchor point (not to the
winch), then pull on the anchored cable in a direction perpendicular to the anchored cable (and you can use the winch in this perpendicular
direction). You can apply a tremendous amount of tension to the almost-straight primary cable in this way, but only up to the tensile yield strength
of the materials. Just size your steel cross sections such that the tensile stress does not exceed, say, 210 MPa.
Regarding a revolving door, almost all web sites fail to understand that the door does not need to be balanced very well at all in order to work well.
It is not an amazing mystery. Open an extremely massive house door. Now barely push it with your little finger. Notice the door rotates effortlessly.
It is completely imbalanced, with hinges far to one side of the door center of gravity, but the door rotates effortlessly.
Nonetheless, this is not to discredit amazing feats. And yet, it seems obvious that many men assisted in the construction. The really amazing thing is
how all of the few people who saw something did not divulge the local secret. Or, if they did divulge it, it has not been widely published (to my