Effects of interparticle force on the packing of spherical granular material

We present a study of the influence of interparticle cohesive forces on the packing of spheres. This is achieved by changing the external magnetic field on iron spheres in the millimeter size range. The force of cohesion between two spheres is measured by opposing magnetic and gravitational force. The void fraction of the bed resulting from many spheres being poured into a container at a given magnetic field is measured. The void fraction of the packed spheres as a function of interparticle force is thus established. We find that the void fraction is determined only by the ratio of interparticle force to particle weight, regardless of particle size. This is shown to be a universal effect, not limited to magnetic systems.