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[Phys-l] ingenious? or just perverse?



Hi Folks --

I recently watch the Mythbusters segment where they built a _lead balloon_.

They seemed particularly pleased with the way they were able to build
the balloon on the flat, and then have it blossom into a cube when
inflated.

The same sentiments are echoed on their fan site:
http://mythbusters-wiki.discovery.com/page/Lead+Balloon
* That unfolding cube was phenomenal.
* My hat is all the way off to Adam for a most awesome feat of very delicate origami.

Google turns up lots of independent sites that praise the "clever design".

Am I the only one who is bothered by this?????

Wait just a minute here!



When I was in elementary school, at the lunch table it was common for kids
to flatten their empty half-pint milk cartons by folding them. There is a
way to flatten a cube that
a) is very simple, and
b) does not stress or stretch the material; it is a natural
origami-style fold. See below for details.

In contrast, the Adam Savage approach
a) involves a 12-step layout process, and
b) seriously stresses the material during the unfolding process
(even though the flat square is stress-free and the /fully/
opened cube is stress-free).


In case anybody is wondering, here is how I would lay out a folded cube,
to be unfolded by inflation:
http://www.av8n.com/physics/img48/folded-cube.png
The layout is built from four pieces, each of the shape shown. The
bottom piece is exactly as shown. Then the two side pieces are made
in the shape shown, but folded in half lengthwise before being joined
to the layout. Then the top piece is exactly as shown. The final
layout is everywhere four layers thick.

Note that if you are compacting a milk carton, you would probably
tuck the triangular end-caps /inside/ ... but if you are building
a balloon and have plenty of room, it is more convenient to leave
them on the outside, as shown.

Meanwhile, the Adam Savage scheme appears to be the following: start
with a five-faced object consisting of a cube that is missing its top.
Crease each of the four side-faces along the diagonal from northwest
to southeast. This is a "valley" crease as seen from outside. Then
collapse the cube with a twisting motion. It works fine for the five
faced object ... which is what they proudly showed on the TV show ...
but if you try it with the sixth face in place it doesn't work nearly
so well.

========================
Philosophical remarks:

I don't mind original approaches, or even eccentric approaches, and other
things being equal I like to cultivate and reward original approaches ...
but let's keep in mind that originality is not the only criterion.
Practicality figures in there also. Here is a diagram that shows
roughly how I think about such things:
http://www.av8n.com/physics/img48/eccentric.png

==========================================================

And don't get me started about the other segment on that episode,
"surfing with dynamite". They might have been able to make that
work if they'd known the first thing about the physics involved.

I doubt that anyone on the team could put together a sentence using
the words "dispersion" "nonlinearity" and "soliton".

One of them even said "it peters out radially, not like waves at
the beach". Well... what did you expect when you set up a
radially-symmetric geometry?

Hint: Famous 150-year-old quote about the basic physics:
http://www.ma.hw.ac.uk/~chris/scott_russell.html