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Title: Granular eruptions: void collapse and jet formation

Description: A steel ball dropped onto loose, very fine sand creates an upward jet exceeding the release height of the ball. It is generated by the gravity-driven collapse of the void created by the ball: the focused pressure pushes the sand straight up into the air. The impact of the ball on the sand bed and subsequent jet formation was visualized using a high-speed camera recording 1000 frames per second. Using a two-dimensional experimental setup, the collapse of the void is visualized. For high impact velocities, the void collapse is seen to entrain air. The entrained air bubble slowly rises through the sand, and, upon reaching the surface, causes a granular eruption.

Credits: René Mikkelsen, Michel Versluis, Elmer Koene, Gert-Wim Bruggert, Devaraj van der Meer, Ko van der Weele, and Detlef Lohse

References:

Web Page: http://pof.aip.org/pof/gallery/video/2002/912209phf_lg.mov

Contributed By: Tausif Billah