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Re: [Phys-l] expand your mind



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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