The wonderful world of granular ratchets Original Research Article

Computer simulation predicts that horizontal size segregation can be obtained in a vertically vibrated layer of granular material. This behavior is a consequence of two distinct phenomena that are unique to excited granular media: vibration which causes the large grains to rise to the top of the layer, and a vibrating base with a sawtooth surface profile which can produce stratified flows in opposite directions at different heights within the layer. The result of combining these effects is that large and small grains are horizontally driven in opposite directions.