Angle of repose

Description

2016 Third Place This image captures a familiar beach activity: pouring sand in a heap. When dropped from above, grains of sand pile up, some sliding down the sides of the growing mound, making a relatively uniform heap. Here, millimeter-sized glass spheres are piling up on a much smaller scale. As the material avalanches from the tube above, individual beads fall and bounce radially away from the center. The surface of the heap forms an angle with the horizontal called the angle of repose. Scientists study this angle to understand the unique properties of the granular medium (like its sliding friction and density). Isner and his colleagues in the Ottino/Lueptow laboratory characterize material behavior like this to understand real world particle flows like grain in silos, and rocks in avalanches and landslides.

Abstract

This image originally appeared as part of Northwestern's Scientific Images Contest. The contest and subsequent exhibitions are organized by Science in Society, the university's research center for science, education, and public engagement. Further information and opportunities to participate are available on their website. Prints and canvas editions of these Northwestern research images can also be purchased online (with the small net profit going to science education and outreach programming in the Chicago area).

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