Quasi 2D granular dynamics

4000 spheres of steel (diameter 2mm) are deposited on a horizontal rough plate (200mm diameter, only a square 100mm X 100mm is shown) and are put in motion by vertical vibration of the plate (sinusoidal shaking, amplitude 0.7mm, frequency 200Hz). The resulting motion, on the plane, is a composition of random sliding on the plate and inelastic collisions among particles. This is a “non-equilibrium” Brownian motion. Laboratory and scientific details. Notice that the image is processed so that bright spots (reflected by steel spheres) represent only a fraction of the area covered by each sphere, giving the illusion that spheres interact without touching.