These Are Bubbles Made of Sand

Engineers observed bubbles of sand moving within other sand, like oil droplets through water, in a first-of-its-kind observation.

It’s difficult for scientists to understand the behavior of countless small moving particles, and we’re still learning new things about materials like sand, as some of our past stories show. In a new experiment, scientists observed two kinds of sands interacting, where one sand would form bubbles in the other sand. Better understanding the movements of these granular materials could lead to important results.

“There are a variety of different motivating factors” for studying how two sands move around one another, study author Christopher Boyce, assistant professor in chemical engineering at Columbia University, told Gizmodo. That includes construction, pharmaceuticals, and even alternative energies.

The experiment consisted of a pair of sands, a white “heavy” sand atop a black “light” sand, in a see-through rectangle. The black sand had slightly larger, but lighter, grains than the white sand. A machine shook the rectangle up and down, while air flows upward through the sand. The researchers observed as granular “bubbles” and “fingers” composed of the lighter black sand flowed upward through the heavier white grains.

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