You might find the Klopsteg Memorial Lecture: " Physics at the Breakfast Table - or Waking up to Physics " by Sidney R. Nagel of interest (American Journal of Physics, 67, (1) January 1999 pp 17-25 ) Also see the Bibliography he gives on the behavior of granular materials. They have quite different modes of behavior!
Ludwik Kowalski <KowalskiL@MAIL.MONTCLAIR.EDU> Wrote:
>A strange observation. I put about 1/3 spoon of coffee (Taster's
>Choice, 100% pure Instant) into a glazed porcelain (clay ?) cup.
>Then about the same volume of Coffee Mate powder (non-dairy
>creamer Carnation, a little package from Nestle).
>
>Before adding hot water I started shaking the cup to mix two
>powders. Brown coffee grains are larger than while "milk"
>powder. NO MATTER HOW LONG I SHAKE I still do not see
>uniformity. White powder particles like to stay together, more
>or less. Two substances mix but not totally. After some shakings
>the mixture becomes nearly uniform but a clear tendency for
>clustering seems to prevail. Shaking seems to do two things:
>mixing and separating big particles from small particles.
>
>My white cup, by the way, has Einsein's face on one side and
>E=m*c^2 on the other. I am sure this is purely coincidental. The
>mean depth of my mixture is about 3 mm or so. The bottom
>is not perfectly flat. An illusion of some kind? A wrong way of
>mixing?
> Ludwik Kowalski