Granular shearing and Barkhausen noise

We present results from a series of experiments on a granular medium sheared in a Couette geometryand show that their statistical properties can be computed in a quantitative way from the assumption thatthe resultant from the set of forces acting in the system performs a Brownian motion. The sameassumption has been utilized, with success, to describe other phenomena, such as the Barkhausen effectin ferromagnets, and so the scheme suggests itself as a more general description of a wider class of driveninstabilities.