Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-l] ingenious? or just perverse?


On Jul 11, 2008, at Jul 11(Fri) 9:15 , John Denker wrote:

Well, all I can say is that I am unable to replicate a "nice"
result. Either we have different notions of what "nice" is,
or I'm doing something wrong.

It seems to me that the word 'nice' is the only problem here.
and hence the 'degree' of crumpling that one accepts.

Here's a photo of what I get when I try it:
http://www.av8n.com/physics/img48/crumple-cube.jpg

I maintain that less crumpling comes from careful folding but crumpling is inevitable - just as it is with your 'nice' design. Your method cannot be constructed from sheet metal with piano hinges. At least not in any way that I have been able to find.

I maintain that zero crumpling = nice = sheet metal + hinges on each fold.

(but this is just my personal take on the word 'nice' in this situation)



I don't want to get into a big debate about the symmetry.
-- If I wanted to make the result symmetric, I could have done so.
-- If I wanted to make the result non-symmetric, I could have done so.
-- When I just fold the cube without thinking about it and without
trying to bias the result, it is not quite symmetric. I get a Z- fold
on two sides, and an L-fold on two other sides. You can see one of
each in the photo.

We agree that the 100% folded state is symmetric and stress-free and
that the 100% unfolded state is symmetric and stress-free. My point
is that when the thing is about 1/3rd open it is under lots of stress
for no good reason.

Your elementary school fold is also under stress as it transitions.
If NOT, please be very specific with your construction.
I'll require shirt cardboard with taped edges at least to convince me.

The elementary school folded cube that _*I*_ grew up with is also called the Water Bomb.
Each face of the cube is fold-free but stress is necessary to open it.

see: http://www.mathematische-basteleien.de/oricube.htm et al.


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

My point remains is that the Savage design does not fold nearly as "nicely"
as the plain old elementary-school fold discussed previously, according
to my notion of "niceness".
http://www.av8n.com/physics/img48/folded-cube.png

The Savage cube has only four folds as opposed to n >> 4 for yours.

The top square of the Savage cube must be rotated 90 degrees as it is folded or unfolded.


If the top and bottom of the Savage design remain symmetric, i.e. square
and flat, then there is lots of compressive stress in the edges that
are destined to become the vertical edges. The causes them to crumple
as shown in the photo. If this were *my* lead balloon, I would be very
unhappy with this ... given that the other scheme is AFAICT in every
way simpler and better.

(this is where opinions differ)

and yes - the Mythbusters are quite aware of their lack of 'Perfect Answers'.
When they mess up - they will revisit and correct any errors.

They are WAY less pretentious than the Smash Lab.
Each Smash Lab episode is couched in 'Let's Save Humanity' with our Awesome Creative Powers' terms

cheers