Model bird flocks that go with the flow

Tiny metal rods can behave like a flock of birds, physicists in India report. Just like flocking birds, the half-centimeter-long tapered brass rods will orient themselves in the same direction and move en masse when sprinkled randomly onto a vibrating bed of millimeter-sized aluminum beads. But unlike, say, logs floating down a river, the rods align themselves without physically touching. Instead, the rods influence one another indirectly, the researchers reported last month in Nature Communications. Each rod takes up energy from the vibration and begins to move. But the jiggling rod then disturbs the surrounding beads and drags them along with it. The motion of the beads then reorients nearby rods, which get dragged along in the flow like weathervanes in the wind, leading to the overall flocklike behavior. The finding could suggest an alternative to the conventional model of flocks, in which a bird aligns itself with its nearest neighbors and not through the surrounding medium.

(Video credit: Nitin Kumar, Harsh Soni, Sriram Ramaswamy & A. K. Sood)