Question

The Navier-Stokes equations are all partial differential equations. What will be the best reason behind this?

(a) Ordinary differentials are not present in the Navier-Stokes equations

(b) The dependent variables are functions of all of the independent variables

(c) Each dependent variable depends on only one of the independent variables

(d) Partial differentials are only present in the Navier-Stokes equations

The question was asked in an internship interview.

My question is from Navier Stokes Equation topic in division Governing Equations of Fluid Dynamics of Computational Fluid Dynamics

Answer 1

The correct option is (b) The dependent variables are functions of all of the independent variables

To elaborate: Each dependent variable in the Navier-Stokes equations depends on all of the independent variables. So, partial differentials are used to indicate that the other independent variables should be kept fixed while differentiating.