High-speed x-ray movies
This set of clips shows what happens inside the granular bed, after the sphere impacted. The bed is illuminated with x-rays at the Advanced Photon Source at Argonne National Laboratory and the transmitted flux is imaged off the detector with a Phantom v7 high-speed video camera. Because the field of view in these experiments is much smaller than the system size, we stitched together the results from independent runs, adjusting the lateral position and the timing so that the collage appears as a continuous event (note that the phenomenon is so highly reproducible that even small details repeat from run to run). The clip on the left shows the phenomenon under atmospheric pressure conditions, where a large jet is ejected. Comparison with the clip on the right shows the strikingly different behavior when the system is evacuated. Because in the latter case the granular material as a whole behaves much more inelastic and compressible, the sphere does not penetrate as far and, furthermore, generates a shock-like compression wave in front of it.
copyright: John Royer, Eric Corwin, Heinrich Jaeger, University of Chicago, 2005