Based on Newton’s third law, the Navier-Stokes equations are derived. When transitioning to dimensionless quantities, the Reynolds number can be introduced, which allows for a classification of flows and thus opens up the possibility of transferring results from simulations. For technical applications, we further distinguish between turbulent and laminar flows, with the latter being our main focus. As a special case of the Navier-Stokes equations in the inviscid-flow approximation, the Euler equations are obtained, from which Bernoulli’s theorem is derived. Finally, equations for vortex propagation are derived, which are also important for explaining aerodynamic lift.