classical Euler's equations of fluid dynamics. A simplified system If one disregards the tangential components of the velocity field, as frequently done in the study of thin fluid film, one arrives at the following simplified system with only two unknowns: the two dimensional density and the normal velocity : References 1. Exact nonlinear equations for fluid films and proper adaptations of conservation theorems from classical hydrodynamics P. Grinfeld, J. Geom. Sym. Phys. 16, 2009 Continuum mechanics Fluid dynamics Fluid mechanics Nonlinear systems Differential geometry Manifolds