Is the following velocity field a possible incompressible flow? \nu (x,y,z,t)=\frac{\rho g\sin \theta }{\mu }\left(yh-\frac{y^{2}}{2} \right)\hat{i} where ρ is the mass density of the fluid, g (=9.81 m/s^{2}) is the gravitational constant, \mu is the viscosity of the fluid, \theta is some fixed angle (number) relative to a horizontal datum, and h is some depth of a fluid film.