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Re: [Phys-L] cantilever photo



Referring to
http://www.sciamanda.com/Anthony.jpg

On 04/05/2017 08:02 AM, Anthony Lapinski wrote:
A French teacher here sent me this photo, which was forwarded to him. No
idea of the location of this building. He asked me if this scenario would
work. Those appear to be heavy bags of sand/concrete on the rooftop.
Considering the fulcrum position of the lever, it might be possible. Still,
it seems unstable and unsafe. The photo looks real, but anything can be
photoshopped these days. Any thoughts?

1) I see no reason to doubt the authenticity.

2) There is no doubt that it is possible. There is no problem
with the physics. The idea of a counterweight + cantilever is
not new or controversial or complicated.
https://sc02.alicdn.com/kf/HTB1LWw_LXXXXXbzXFXXq6xXFXXXU/Second-Hand-Tower-Crane.jpg

3) One can criticize the engineering details. There are stability
issues and safety-margin issues. For one starters, each pile of
sandbags looks unduly tall compared to its width. The pile near
the upper-left corner looks like it's made of numerous small
sandbags, which seems particularly sketchy.

If I were doing it, I would use rope to lash each sandbag to the bean,
to absolutely eliminate any risk that a single event (such as toppling)
could cause a disaster.

Rope is cheap. The effort required to lash the sandbags in place
is trivial compared to the effort required to schlep all the
materials up to the roof. Proper knot-tying requires some skill,
but it's certainly doable.

Outstanding reference:
https://archive.org/details/TheAshleyBookOfKnots