Footprints in sand: The response of a granular material to local perturbations - art. no. 035506

We experimentally determine ensemble-averaged responses of granular packing s to point forces, and we compare these results to recent models for force propagation in a granular material. We use 2D granular arrays consisting of photoelastic particles: either disks or pentagons, thus spanning the range from ordered to disordered packings. A key finding is that spatial orderin g of the particles is a key factor in the force response. Ordered packings have a propagative component that does not occur in disordered packings.