The attraction of Brazil nutsD. A. Sanders, M. R. Swift, R. M. Bowley and P. J. King
School of Physics and Astronomy, University of Nottingham Nottingham, NG7 2RD, UK
received 2 September 2005; accepted in final form 9 December 2005
published online 4 January 2006
Simulations of intruder particles in a vertically vibrated granular bed suggest that neutrally-buoyant intruders are attracted to one another (Phys. Rev. Lett., 93 (2004) 208002). The simulations, however, ignore important physical effects such as friction and convection which are known to influence intruder behaviour. Here, we present experimental evidence for this intruder-intruder interaction, obtained by monitoring the position of neutrally-buoyant metallic disks in a vibrated bed of glass spheres. An effective long-range attraction is shown to exist between a pair of intruders for a range of driving conditions. If further intruder particles are added, a tightly bound cluster of intruders can form. These results highlight the difficulty of retaining well-mixed granular beds under vertical vibration.
45.70.-n - Granular systems.
45.70.Mg - Granular flow: mixing, segregation and stratification.
© EDP Sciences 2006