Hi Dan,
Yeah, they aren't solids, yet they also don't follow Newton's
definition of fluids either. Basically, a fluid is called non-Newtonian
if its viscosity depends on the force that is applied to it.
As you might know, viscosity is a measure of how easily a fluid
flows (the higher the viscosity, the harder it would be to stir a bowl
full of it). For example, water has a lower viscosity than syrup. For
an ordinary fluid (like water) the viscosity wouldn't depend on how
fast you were stirring it, but for a non-Newtonian fluid it would.
Depending on the specific non-Newtonian fluid you had, it could get
easier or harder when you tried to go faster. It's very cool
actually... imagine something that would bounce a little if you dropped
it (a very sudden impact force when it hits the floor), but that would
get sort-of watery if you just held it in your hand. I had never heard
that toothpaste was a non-Newtonian fluid, but if you do an experiment,
definitely let us know the result. You can make your own non-Newtonian
fluid by blending cornstarch and water together until it forms a syrupy
mixture (try it). Let us know if you find some other examples.
Cheers Jesse
(published on 10/22/2007)
