Re: [Phys-l] expand your mind

[Brian Whatcott <betwys1@sbcglobal.net>]

Use another comparable model.   A can of polyurethane foam.
If you spray a ring of that foam and wait, the inner edges may
 close up, and touch. A question of a plastic material yielding to
a motivating gas.

Brian Whatcott

At 11:41 AM 2/23/2006, you wrote:
> I know why the metal hole expands. Why does the bagel hole contract?
>
> Forum for Physics Educators <phys-l@carnot.physics.buffalo.edu> on
> Thursday, February 23, 2006 at 11:17 AM -0500 wrote:
> >Think about the atoms in the edge of the inner ring.  The increased
> >temperature means that each on the average take of more space, but
> >moving in would decrease the circumference and hence force the atoms
> >closer together rather than further apart.  Now it could happen if
> >the material folded.  In a metal that means creating
> >dislocations...that takes more energy than is available, but bagels
> >are another thing.
> >
> >Does that help...comments?
> >
> >joe
> >
> >Joseph J. Bellina, Jr. Ph.D.
> >Professor of Physics
> >Saint Mary's College
> >Notre Dame, IN 46556
> >
> >On Feb 23, 2006, at 11:09 AM, Anthony Lapinski wrote:
> >
> >> In discussing heat, I did the ball/ring demo and many students were
> >> surprised to see that the hole EXPANDS when the ring is heated.
> >> It's like
> >> expanding a photograph of a bagel -- both the inner and outer
> >> diameters
> >> expand. So a student today asked why actual bagels behave differently.
> >> When the yeast is settling, 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? This
> >> question has never come up before, so I thought I'd ask the experts
> >> (since I don't eat bagels much!).
> >>
> >> _______________________________________________
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> >> Phys-l@carnot.physics.buffalo.edu
> >> https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l
> >
> >_______________________________________________
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> >https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l
>
>
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Brian Whatcott    Altus OK    Eureka!