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Re: [Phys-l] expand your mind



Other than the pleasure of making and eatin a fresh bagel, it is really not necessary to investigate friction. Since bagels rise on a greased sheet, the friction is already quite low. The folding of the innner edge of a bagel clearly shows that it takes less energy to fold and crumple than to stretch the dough. Folding and crumpling is not possible with a metal ring, and unlikely with an innertube. It might be interesting to investigate how much the bagel expands by lightly coating the bottom with a ring of colored stuff (food coloring) and then by looking at the color trace on the greased sheet.

Also the account of the center getting smaller has not been verified experimentally. I would suspect that it may not happen uniformly the same for all bagels. This is a great opportunity for making and consuming lots of bagels with cream cheese or whatever. Personally I will stick to buying mine from the good bagelry in town.

John M. Clement
Houston, TX



constrained by friction against whatever it's sitting on while it rises.

Here's a simpler way to minimize friction during rising: Build a
"bagel boat" by cutting a piece of buoyant wood (e.g. balsa wood)
into N pieces:
http://www.av8n.com/physics/img48/bagel-boat.png

It's like an ordinary raft, except that it has _expansion joints_
between the pieces.

Put the not-yet-risen bagel on the bagel boat, and then float it
in a shallow dish of water.

This should allow it to expand more-or-less isotropically ... so
that the hole in the middle expands as everything else does.

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

Also, to minimize memory effects due to internal stress, two
possible lines of attack:

1) Make a big flat sheet of dough and cut out an annulus using a
donut cutter (or knife or scissors); or

2) If you like to build your bagels by creating a cylinder and then
joining the ends to make a torus, proceed as usual but make the
cylinder N times thinner (and therefore N^2 times longer), where
N is at least 2 and preferably greater. This may well require
making several separate strands, rather than one reeeally long
one. Then build the bagel by wrapping the strands around and
around and around. (Optionally you can get artistic with this
if different strands have different properties: whole wheat
versus not, cinnamon in the dough versus not, et cetera.)


*) Keep in mind that the goal is to minimize internal stresses,
or at least to make the stresses homogeneous and isotropic.
homogeneous == same everywhere
isotropic == same in all directions
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