# What are the assumptions of the Navier-Stokes equations?

I wanted to model a real life problem using the Navier-Stokes equations and was wondering what the assumptions made by the same are so that I could better relate my entities with a 'fluid' and make or set assumptions on them likewise. For example one of the assumptions of a Newtonian fluid is that the viscosity does not depend on the shear rate. Similarly what are the assumptions that are made on a fluid or how does the Navier-Stokes equations define a fluid for which the equation is applicable?

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Are you asking what assumptions you can make to reduce the Navier-Stokes equations? Or are you asking, to what can the Navier-Stokes can be applied? –  Kyle Kanos Sep 24 at 15:58
It assumes the stress in the fluid is the sum of a diffusing viscous term (proportional to the gradient of velocity) and a pressure term. See here en.wikipedia.org/wiki/Navier%E2%80%93Stokes_equations –  Shuchang Sep 24 at 15:58
This might be extremely obvious, but the fluid must be reasonably approximated by a continuum. See Knudsen Number. –  OSE Sep 24 at 16:20
@Kyle The latter –  Rohan Prabhu Sep 25 at 5:57