Revealing the secrets of sand

Brandeis scientist receives $1 million to explore the behaviors of macroscopic assemblies

Photo/Mike Lovett

Bulbul Chakraborty

Next time you’re at the beach, scoop up a handful of sand and watch how it flows like water through your fingers. Then, look at the rolling sand dunes beyond the towels and umbrellas. The sand in your hand and the sand in the dunes is the same material. But one acts like a liquid and the other, a solid.  

How is that possible? The truth is, scientists don’t know. 

Physicists use a fundamental theoretical framework to predict how a large collection of small molecules can flow as a liquid or freeze into a solid. Yet they have little understanding of the forces that create sand dunes or trigger an avalanche. Scientists lack fundamental concepts to describe how assemblies of macroscopic objects — sand, snow, grains, rocks or jellybeans — form and respond to stress. 

Bulbul Chakraborty, the Enid and Nate Ancell Professor of Physics, hopes to change that. Chakraborty, along with Corey O’Hern from Yale University and Robert Behringer from Duke University, have received a three-year, $1 million grant from the W.M. Keck Foundation to develop the first predictive theoretical framework to characterize behaviors of macroscopic assemblies.    

The team will focus on jamming, a common — and sometimes deadly — behavior of macroscopic assemblies, from traffic snarls to corn silo bottlenecks. Even jellybeans in a bottle turned upside down flow like water until they jam.  

“The transition from the flowing to the jammed state is not understood well enough to be predictable,” Chakraborty says. “The process of jamming and the properties of jammed states are at the heart of all granular science. Jamming affects all industrial granular processing and has a huge impact on natural events.”  

To transport large quantities of grain, for example, agricultural engineers rely on machinery that keeps the grain flowing; otherwise, jammed grain can lead to a burst silo and millions of dollars in lost crop. On the other hand, deadly avalanches can result when snow fails to jam. 

“This research has broad implications for energy, such as in transporting coal; for agriculture, and for designing for avalanche and earthquake prevention systems,” Chakraborty says. 

Keep that in mind, next time you’re at the beach. 

Categories: Research, Science and Technology

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