READING #5 - Experimenting with Sand

Piotr Habdas and Eric R. Weeks, Physics Department, Emory University, Atlanta, GA

In our lab, we use various microscopy techniques to look at small colloidal particles (few thousands of a millimeter in diameter) suspended in a liquid (just like Robert Brown almost 200 years ago). We study how their motion changes when the particle concentration You have probably played before with sand on a beach or in a sand box, but you have probably never thought about the rich behavior that the sand exhibits. By changing external conditions you can watch the sand behave differently. For example, if you put some sand on a table in a pile it sits there just like any other solid. But if you start to tip the table to some angle the grains begin to flow just like a liquid. If you start moving your arms up and down very quickly while holding the table with the pile in your hands the sand particles will start flying off in all directions just like in a gas.

You may ask yourself a question: why is understanding of sand behavior so important? Why have the physicists been studying sand so eagerly? Obvious answer would be that physicists like to study anything that they don't understand. But there is more to that. Understanding sand behavior has enormous implications in industry. Understanding granular materials is relevant for:

In the Experimenting with Sand lab you will get a chance to look more closely at this so called granular media, called by some scientists the fourth state of matter (in addition to liquid, solid and gas).