So i am working on a program that models the movement of a rocket through different planets. and i sm starting to get teach my self fluid dynamics. As i was reading a presentation by nasa about the forces that act on a rocket they got into shape effects on drag, i noticed from their equation Cd = D/(r * A * (V^2)/2) " The drag coefficient is a number which aerodynamicists use to model all of the complex dependencies of drag on shape inclination, and some flow conditions. The drag coefficient (Cd) is equal to the drag (D) divided by the quantity: density (r) times reference area (A) times one half of the velocity (V) squared. " does not include the surface friction aspect of the problem, why is that, is this a simplified equation?