July 10, 2006

Singing Sand Solved

Posted by Arcane Gazebo at July 10, 2006 3:58 PM

An interesting paper appeared in PRL a few days ago on the phenomenon of "singing sand" (I've also heard it called "booming sand"). Sand dunes in certain locales are known to produce sounds at particular frequencies, with the frequency apparently depending only on the size of the grains of sand. One can take a sample of sand out of the dunes (perhaps in Capt. Sparrow's jar of dirt) and reproduce the sound from it. This was a classic modeling problem in Caltech's Ph 11 class, but in this PRL the researchers actually did some experiments and found that the sand produces self-synchronized waves.

Song of the Dunes as a Self-Synchronized Instrument

S. Douady, A. Manning, P. Hersen, H. Elbelrhiti, S. Protière, A. Daerr, and B. Kabbachi

Since Marco Polo it has been known that some sand dunes have the peculiar ability to emit 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 singing dunes around the world and two controlled experiments, in the laboratory and the field, we prove that the frequency of the sound is the frequency of the relative motion of the sand grains. Sound is produced because moving grains synchronize their motions. The laboratory experiment shows that the dune is not needed for sound emission. A velocity threshold for sound emission is found in both experiments, and an interpretation is proposed.

Tags: Physics, Science

Melany Hunt of Caltech has been very active studying such things.

Posted by: Mason Porter | July 11, 2006 1:29 PM
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