| Granular materials, like sand, sugar or salt, are composed of many particles that can move independently. The study of the statistics and dynamics of these systems requires new theoretical ideas beyond those in the standard statistical mechanics, hydrodynamics or traditional solid mechanics. Granular materials differ from standard molecular materials in that frictional forces among grains quickly dissipate energy and drive the system toward frozen or glassy configurations.; In this work I will present new experimental results regarding the forces opposing the movement of macroscopic objects through dense granular materials. I will show that this drag is caused by the successive formation and collapse of jammed states, which results in large stick-slip fluctuations in the force. Another interesting result presented in this work is that, in quite contrast with the expectations, neither the surface properties of the dragged objects nor their shape has affected significantly the average value of the drag—thus implying that the stress induced collapse is nucleated in the bulk of the granular sample. |
