The laws that govern fluid dynamics generally seem outside the intuitive grasp of many people. In this module we begin with a simple analogy which puts the complex content of this often scary topic in terms of a story to which everyone can relate. From this analogy, not only are general fluid dynamic principles appreciated, but also the foundation of the fluid dynamic equations is derived. Further use of analogies and thought experiments will then allow us to derive all of the equations needed, including the resistance equation, the simplified law of hemodynamics, the continuity equation, Poiseuille's Law, and the Bernoulli equation. Once the equations are derived, we develop a conceptual appreciation of the equations through direct application in various clinical situations. Finally, we will learn how to relate the Doppler spectral characteristics with the hemodynamic concepts just learned.