Synopsis: Bird Flocks Shatter on Impact

Simulations show that flocks hitting a wall disintegrate like brittle solids rather than splash like fluid drops.
Synopsis figure
N. Ouellette and P. Miller, Phys. Rev. E (2014)

Flocking birds are well known for their magnificent swarming behavior, where thousands of individuals move as one entity. These flocks have clear boundaries, which seemingly hold the birds in. Researchers typically model such collective systems by representing each bird as a self-propelled particle, with neighboring particles coupling by aligning their velocities. The dynamics of the flocks can then be simplified and analyzed in terms of traditional “flowing” material properties. This has led Nicholas Ouellette and Pearson Miller at Yale University to question what would happen if the flock flew into a wall. From its fluidlike behavior, you might expect it to splash like a raindrop. Writing in Physical Review E, Ouellette and Miller show instead that impacting flocks shatter like brittle solids.

In their simulations, the team started with a well-defined flock and drove it towards a solid wall. Initially, the impacting flock flattened into a pancake, compressing against the wall. Individuals at the front rebounded off the wall, disrupting the oncoming flock. This process continued until most of the particles were moving away from the wall and the original flock had broken into distinct smaller clusters. By studying the size distribution of the clusters, Ouellette and Miller were then able to infer the material properties of the flock on impact—splashing liquids break up into droplets of similar size, while brittle solids split into pieces of all sizes. The authors saw the latter, suggesting that the flock behaved as a brittle solid, rather than a splashing droplet. – Katherine Wright


More Announcements »

Subject Areas

Complex Systems

Previous Synopsis

Next Synopsis

Related Articles

Focus: Wikipedia Articles Separate into Four Categories
Interdisciplinary Physics

Focus: Wikipedia Articles Separate into Four Categories

A study of the entire editing history of English Wikipedia shows that the articles cluster into four categories based on how frequently and how aggressively they are edited. Read More »

Synopsis: Fractal London
Statistical Physics

Synopsis: Fractal London

An analysis of London’s street network shows how the network has evolved over time from a heterogeneous to homogeneous fractal pattern. Read More »

Viewpoint: Microbial Ecosystem Follows Deterministic Dynamics
Biological Physics

Viewpoint: Microbial Ecosystem Follows Deterministic Dynamics

High-resolution tracking of the population abundances in a simple, closed microbial ecosystem shows that the intrinsic dynamics of the system are strongly deterministic. Read More »

More Articles