Musical Sand

Abstract

Since last century, a number of investigations were reported on the peculiar sound producing beach or desert sands. The so-called musical sand, which emits a musical sound when walked on, can be found in several parts of the world. A long time ago, many Japanese beaches were known as musical one. However, recently almost all the beaches have lost the peculiar properties with pollution attributed to various human activities. Various fine dusts and oily materials adhered to the surface of the sand grains. If additional influx of polluted materials had been stopped for a very long period of time, they would have been cleaned up by the mechanical washing action of sea wave, so-called beach action, in natural environment. Laboratory experiments were conducted in an attempt to simulate the natural process. For this purpose, gyratory motion washer was used, because the movement speed and pattern of water and sand were nearly similar to beach action. The washed sand had excellent sound producing properties and pronounced not only in the air but also in the water. The perfectly cleaned up sand was characterized by very high friction coefficient of the sand layer, so the penetration test of the sand layer showed clear stepwise characteristics, resulting from significant difference of static and dynamic friction coefficient. Moreover, from the correspondence of the wave form of sound pressure and stress in sand layer, an explanation of sound producing mechanism was described.