Intermittent flow, jamming, and Beverloo's law in granular systems
Granular materials (sand, grain) flow through hoppers intermittently — they jam and unjam. Beverloo's law (1961) gives the average flow rate:
Q = C · ρ · g^½ · (D − kd)^(5/2)
where D is orifice size, d is particle diameter, and k≈1.4 is the "empty annulus" factor. Unlike liquids, flow rate is independent of fill height — a key signature of granular flow.