Precise simulations of the movement and behavior of crowds can be vital to the production of digital sequences or the creation of large structures for crowd management. However, the ability to quantitatively predict the collective dynamic of a group responding to external stimulation remains a largely open issue, based primarily on models in which each individual’s actions are simulated according to empirical behavioral rules. Until now, there was no experimentally tested physical model that describes the hydrodynamics of a crowd without assuming behavioral rules.