Granular Rods Fall Faster in Denser Obstacle Fields

How particle shape affects transport through obstacle fields under external driving is a fundamental question in nonequilibrium physics. We simulate a dissipative rod falling under gravity through randomly placed fixed obstacles. As the obstacle density increases, the mean descent speed decreases, increases, and then decreases again before trapping. The rod can therefore fall faster in a denser obstacle field. Scaling arguments based on collision rates and rod geometry explain all three regimes, their crossovers, and the mean fall distance before trapping. These results reveal nonmonotonic driven transport arising from particle anisotropy.