SHAKE, RATTLE, and ROLL: The Physics of Granular Media

Andrew Dougherty

Physics Department
Lafayette College

ABSTRACT

Is sand a solid, a liquid, both, or neither? It can be poured like a liquid, and it can also support weight like a solid. But counting on either behavior can lead to disaster: Flowing sand can clog a pipe and structures built on sand tend to lean and topple.

Granular materials often exhibit surprising non-intuitive behavior with important consequences for a wide range of applications. In this talk I will discuss some current aspects of research involving granular materials.

I. SHAKE, RATTLE, AND ROLL: Mixing and Demixing

A. Why the Brazil Nuts come out on Top.

1. Larger objects ``float'' to the top.

2. Importance of Voids.

3. Reverse Buoyancy?

B. Segregation in Flows.

C. Drum Mixers.

II. CASTLES IN THE SAND.

Can sand act as a solid foundation? How are forces transmitted through sand?

A. Shaky supports.

B. Arching and Force Structures.

III. LIKE SAND THROUGH THE HOURGLASS . . .

Granular materials do often flow, but not necessarily like water.

A. Hourglass.

B. Clustering.

C. Convection.

D. Vibration.

E. Sand Ripples.

IV. SANDPILES and AVALANCHES.

Avalanches, power laws, self-organized criticality and theories about nearly everything, including evolution and the stock market.