Are Brazil Nuts Attractive?

Duncan Sanders

School of Physics and Astronomy University of Nottingham, University Park, Nottingham NG7 2RD, U.K.

We present event-driven simulation results for single and multiple intruders in a vertically vibrated granular bed. Under our vibratory conditions, the mean vertical position of a single intruder is governed primarily by a buoyancy-like effect. Multiple intruders also exhibit buoyancy governed behaviour; however, multiple neutrally-buoyant intruders cluster spontaneously and undergo horizontal segregation. These effects can be understood by considering the dynamics of two neutrally buouyant intruders. We have measured an attractive force between such intruders which has a range of five intruder diameters, and we provide a simple mechanistic explanation for the origins of this force.