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Take a look at Kinetic Carnival of Physics - Jearl Walker.
In it he talks about Isotropic Fluids - the corn starch and water
phenomena.  Plus he seems to suggest that all mixtures of solids and fluids
(including sand in air), quicksand, beach sand that is water saturated and
even solid particles suspended in air exhibit these properties - but to a
greater or lesser extent depending on the materials.
My rather limited understanding is that essentially, when put under high
shearing pressures the particles make contact with one another in a jumbled
arrangement acting as a solid (essentially certain angles of the particle
make contact with other particles while other spaces are left free (and
water goes into those spaces)).  However when left alone the water allows
the particles to flow into more naturally occurring arrangements and the
particles slip over one another with a layer of fluid between them - acting
as a fluid.  So when not under pressure the fluid aspect takes over the
material and particles glide over one another in a more orderly fashion.
 By varying the degree of pressure you vary the solid/liquid
characteristics exhibited.  I have also been told that this is more
complicated with corn starch because it has long chain molecules (like
spaghetti) so exhibits the characteristics even "more so" do to its polymer
style nature.  Of course, I don't know if that's true or not (but it makes
sense to me).


William Katzman                    "The important thing is to never stop
questioning." -A. Einstein
Director of Exhibits               "Are you sure about that Al?" -His wife.
Catawba Science Center
ph: (828) 322-8169 x307
fax:(828) 322-1585
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