This paper deals with an introduction to the momentum balance equations (the generalized Darcy equations) for high Reynolds number flow in porous media as occurring in many industrial applications. The presentation is not based on volume averaged quantities, as is usual in the literature on low Reynolds number flow in porous media, but on so-called `approximate values`. In this way it is possible to direct all attention to the constitutive expressions for the so-called resistance force, and to the related concept of permeability. The theory unifies fluid dynamic theory of drag and lift (in non-porous media) with the conventional theory of fluid flow in porous media.