Wake up, sheeple! You may think you're in charge of your own destiny, but when exiting a crowded stadium, we're all fairly sheeplike, following the flock and perhaps jostling a bit to get to the front. Sheep therefore make a good model to understand crowd behavior in humans. To study how the wooly ungulates move in unison, researchers videotaped flocks of sheep entering a barn door to be fed. Predictably, the animals all scrambled to get in simultaneously, causing a farmyard traffic jam that slowed their progress through the door, shown in the video above. As one might expect, when researchers widened the door, the congestion diminished. But a less obvious strategy had the same effect, the researchers explain in a paper published in the current issue of Physical Review E. Namely, they placed a wide post in front of the door that forced the sheep to go around either side. Scientists previously discovered this method of preventing blockages in flows of granular materials like sand, which exhibit some of the same dynamics as the motion of crowds: Pack too many sand grains into one space and they freeze up like a solid, instead of flowing smoothly like a liquid. By studying flows in systems like sand and sheep, scientists hope to find strategies for designing buildings to prevent dangerous human crowd situations, like stampedes.
(Video credit: A. Garcimartín, J. M. Pastor, L. M. Ferrer, J. J. Ramos, C. Martín-Gómez, and I. Zuriguel)