People in a very dense crowd move in small circular 鈥渙rbits鈥�, like charged particles moving in a magnetic field. The unexpected discovery may help lead to improved mathematical descriptions of dense crowds, which could help us better understand why crowds sometimes move in a way that can lead to people being injured.
at ENS de Lyon in France and his colleagues studied videos of the dense crowds that form at the opening of the San Ferm铆n festival in Pamplona, Spain, .
They used video processing tools to determine the speed and direction of movement of roughly 5000 people in the very dense crowd, which was confined to the 20-by-50-metre town square.
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The researchers then set out to derive a set of equations that could explain the movement patterns they saw in this data. Bartolo says that key mathematical ingredients were applying Newton鈥檚 laws, accounting for the force of friction with the ground and accounting for the fact that the crowd does not move in any overall preferred direction.
One solution of those equations was motion in orbits that mimicked how charged particles move in small loops when they enter a magnetic field 鈥� essentially, groups of people moving in small circles, each of which took on average 18 seconds to complete.
鈥淚 didn鈥檛 expect this at all, and I watched the videos [of the festival] all the time,鈥� says at ENS de Lyon, who worked on the project.
Bartolo in Minneapolis, Minnesota, on 7 March.
But many questions remain, says team member , also at ENS de Lyon. One is whether and how waves may propagate through the crowd, or if the crowd鈥檚 behaviour is more akin to particles in a solid than the fluid-like motion seen in a crowd of marathon runners.
Ultimately, Bartolo and his colleagues want to mathematically predict when crowd motion may become dangerous and lead to injuries. 鈥淚鈥檓 confident that we will produce results that could be really helpful for engineers that are actually monitoring crowds,鈥� he says.
