> Why is fluid dynamics considered to be an effective model when we haven't even proven the soundness of the navier-stokes equations? Fluid dynamics is a field

> Why is fluid dynamics considered to be an effective model when we haven't even proven the soundness of the navier-stokes equations? Fluid dynamics is a field of study, not any kind of model. Navier-Stokes is just what you get when you apply F=ma to Newtonian fluids.