My hypothesis is that the bagel particles are less constrained than the
metal atoms.
Here is a project: take a dry sponge and cut out two shapes in the form
of a ring. Then take one of the rings and cut them up into tiny pieces
and rearrange the pieces in the form of a ring again. Then, add water.
My prediction is that the single piece will expand such that the hole
gets bigger but that the pieces will expand such that the hole gets
smaller.
Alternatively, take a bunch of little metal balls (like ball bearings)
and arrange them side-by-side as to form a ring. Then, heat them up.
As they expand, will they all move away from the center in a uniform
way, maintaining the ring, or will some of them move out and some move
in? My prediction is the latter.
BTW, I haven't tried either one.
____________________________________________________
Robert Cohen, Chair, Department of Physics
East Stroudsburg University; E. Stroudsburg, PA 18301
570-422-3428; www.esu.edu/~bbq