The
cornstarch mixture is known as a colloid (this means "glue"
in Greek) - it is made up of solid cornstarch particles suspended
in water. (A suspension is different from a solution - a solution
of something involves it being dissolved into the liquid, but in
a suspension it remains as a solid and is only mixed up with the
liquid.)
Many, many years ago, Issac Newton came up with some properties
which a liquid should have - cornstarch and water doesn't behave
as it should if it were truely a liquid, so its known as a non-Newtonian
fluid. It is really viscous and when you hit it or try to move
through it fast, it becomes even more viscous. It can act as both
a liquid and a solid - when you stir it or let it run through
your hands, its a liquid but when you hit it, the particles freeze
in place like a solid.
The long chains of cornstarch are a bit like a tangle of spaghetti
in water - when you whack it, the chains all line up and act like
a solid but if you're gentle, you can run it through your hands
like a liquid. Ketchup is another example of a non-Newtonian fluid
and this is why it gets it out of the bottle slower if you start
hitting the bottom of the bottle in a fit of impatience. Quick
sand is similar, the faster you try to escape, the harder it is
to move.
