March 2008

Mysterious Sand Music

Since Marco Polo it has been known that some sand dunes have the peculiar ability of emitting a loud sound with a well defined frequency, sometimes for several minutes. The origin of this sustained sound has remained mysterious, partly because of its rarity in nature . It has been recognized that the sound is not due to the air flow around the dunes but to the motion of an avalanche , and not to an acoustic excitation of the grains but to their relative motion By comparing several singing dunes and two controlled experiments. […]The sound is produced because some moving grains synchronize their motions. The existence of a velocity threshold in both experiments further shows that this synchronization comes from an acoustic resonance within the flowing layer: if the layer is large enough it creates a resonance cavity in which grains self-synchronize. [ powered by Click ]

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