In this section of the course we have investigated several powerful ideas. Dimensional analysis can be used to find equations governing a wide range of problems, as well as to check equations. In the form of the Buckingham method it can be used to generate dimensionless groups which describe the flow in a size-independent manner. These groups, and the idea of dynamic similarity, enable us to extrapolate information from experiments on models to real flows. They are also a fundamental part of the way we think about fluid dynamics, describing types of flow (turbulent, laminar, sub- or super-critical) and relating to the solution of the Navier Stokes equations.