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Re: [Phys-l] expand your mind



Maybe I'm missing something, but aren't bagels boiled? That's pretty low
friction!

Bob at PC

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu
[mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of John Denker
Sent: Thursday, February 23, 2006 1:02 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] expand your mind

Anthony Lapinski wrote:
... So a student today asked why actual bagels behave differently.
When the yeast is settling,

Settling? That means rising, right?

the bagel hole gets SMALLER. As a class we
reasoned that the gas in the yeast releases pressure which expands the
bagel. But why is this behavior different from heating a metal ring?

I hypothesize it's partly -- perhaps entirely -- because the bagel is
constrained by friction against whatever it's sitting on while it rises.

This leads to an obvious prediction: A bagel rising in zero gravity
would _not_ exhibit hole-shrinkage.

And a slightly dodgier prediction: A bagel supported on an ultra-low
friction surface would exhibit markedly less hole-shrinkage than
normal, possibly none at all.

Here's an off-the-cuff idea for an experimental setup: suspend a
not-yet-risen bagel from a bunch of long threads poking through
it. Use enough threads so that it doesn't sag too much between threads.
Use a button or something on the end of each thread if needed to keep
the thread from pulling out. If the threads are long enough, the bagel
as it rises can do whatever it wants horizontally, due to near-infinite
mechanical advantage. Take measurements and pictures before & after
rising.

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