Definition: Hydrodynamics is the study of how well water flows over a shape/surface. It is used in the manufacture of ships and boats where designers have to think about what kind of hull shape will help the flow of water around the vessel; if the brow of the ship is too wide it will meet more resistance from the water which will slow it down; make the angle of the brow more acute and the water will flow over it more easily. The same is true of submarines; hydrodynamics determines the shape of the hull so that the submarine can pass more easily through and under the water.