On 8/10/06, Gerhard Fiedler <lists@connectionbrazil.com> wrote:

> Let's say you have a big chunk of metal. And let's say you take a flame to
> the immediate neighborhood of the hole. And let's say the chunk itself
> (farther away from the hole) stays at room temperature; only the area
> around the hole gets heated. Does the hole get bigger?

If you take a straight piece of metal and heat it, it will get longer.

Everyone can agree on this, right?

If you take the same piece of straight metal, bend it into a ring, and
heat it, it will *STILL* get longer.

Circumference = 2 * PI * R

So, if the circumference is getting bigger, it's radius must also be
getting bigger.  The hole expands.

If you heat the middle (containing a hole) of a piece of metal, it will
expand.  But the rest of the piece isn't getting out of it's way to
make expansion easy.  This introduces stress in the piece of
metal.

Bill

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