What is it about?
This study explores how granular media—from natural sands, to food or medical powders—flow when they're suspended by air and stirred. It is known that these materials can behave like solids, liquids or gas, depending on how much they're pushed or shaken, but it's been hard to describe all these behaviors in one single model. The authors created a "mini-sandstorm" in the lab by blowing air through a bed of grains and then stirring them while recording the force needed. They observed how the grains flowed under different conditions—sometimes like water (smooth), sometimes like toothpaste (sluggish), sometimes like an avalanche (wild and fast). They found that two key quantities could explain all the changes in behavior. Even better: a theory borrowed from studies of glasses helped them capture all these behaviors in one equation.
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Why is it important?
Granular flows are everywhere: in industry (like mixing powders), in nature (like landslides and volcanoes), and even on other planets and small space bodies (Mars, Moon, asteroids). But unlike regular fluids like water or oil, granular particles don't always follow the rules—or rather, we do not yet know exactly the rules they follow. Understanding how granular materials flow when agitated can help us: - design safer factories and industrial process that are more efficient, reducing economical and ecological costs; - predict natural hazards like volcanic flows or debris avalanches; - prepare for space missions that need to deal with dusty surfaces like the Moon or Mars. This work brings us closer to treating granular flows with the same precision as ordinary fluids, which opens the door for more accurate simulations and predictions.
Perspectives
This study bridges the messy world of granular matter with the physics of glasses. It shows that even complex-looking granular flows can be tamed with the right lens. In the future, this approach could be extended beyond sand to include biological materials or active matter—like cells, crowds, or robotic swarms. It also sets the stage for developing more accurate numerical simulations, which can be used to predict complex phenomena, including in environments where we cannot make many a lot of experiments (for example, for space exploration, volcanic flows, avalanches). Ultimately, this work is a step toward a unified theory of "messy matter"—materials don’t always follow our expectations, and yet shape much of our world and beyond.
Olfa D'Angelo
Read the Original
This page is a summary of: Rheological Regimes in Agitated Granular Media under Shear, Physical Review Letters, April 2025, American Physical Society (APS),
DOI: 10.1103/physrevlett.134.148202.
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