Self-Organized Criticality in a Bead Pile

Timothy Sir Louis

The theory of self-organized criticality was introduced as a new way of looking at complex dynamical systems. This theory suggests that systems which naturally evolve to their critical state will exhibit similar behaviors. One of these behaviors is the distribution of the events that occur at the critical state, which is expected to exhibit a power-law behavior. This experiment looks at the distribution of avalanches that occur in a bead pile when the pile is periodically perturbed by the addition of beads. The avalanches are measured by monitoring the mass fluctuations of the pile using an electronic balance. Glass, steel and plastic beads are used to create the piles, which are studied to see if the distribution of avalanches does follow a power law. It was found that the power-law behavior was prevalent in bead piles using all three types of beads. It appears that there is a power law for glass beads, and a separate power law for steel beads. For plastic beads, it seems as if the distribution of avalanches follows two different power laws.


The beads are dropped onto the pile by a bead dropper. The mass of the pile is monitored by an electronic balance. A collection bin catches the beads as they fall off the pile.