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.