Fluid dynamics refers to a subcategory of the science of fluid mechanics, with the other subcategory being fluid statics. While fluid statics deals with fluids that are at rest, fluid dynamics is concerned with fluids that are in motion. Any matter in a gas or liquid state can be considered a fluid. Fluid dynamics is a discipline with many relevant applications in our modern world, most notably because it contains the study of aerodynamics, and also because it comprises part of weather prediction. A typical fluid dynamics problem may include such variables as velocity, temperature, and density.
All of the physical sciences, including fluid dynamics, are governed first and foremost by the laws of conservation. These state that the total amounts of energy, mass, and linear momentum in a closed system remain constant, and that energy and mass can neither be created nor destroyed. That they may change forms, it is true, but they cannot disappear or come from nothing. These laws constitute some of the most basic assumptions in science.
Another governing principle of fluid dynamics is the continuum assumption, also called the continuum hypothesis. While fluids are known to be composed of microscopic, discreet particles, this hypothesis states that they are continuous, and that their properties vary evenly throughout. This often serves as a helpful mathematical approximation, even though it technically ignores one of the basic characteristics of fluids.
Before the invention of powered flight and aircraft in the 20th century, the term hydrodynamics was often used interchangeably with fluid dynamics, because most of fluid mechanics was devoted to studying liquids in motion, rather than gases in motion. When traveling by aircraft became more common, the need developed for these machines to be more efficient at creating and maintaining lift, with a minimum of drag. The branch of study known as aerodynamics made leaps and bounds because of the new technology, which has also come to be applied to automobiles, to some extent, with the goal of increased fuel efficiency.
One of the more important figures in modern aerodynamics was Octave Chanute. In addition to compiling a comprehensive volume of the study of aerodynamics in the late 1800s, he personally assisted the Wright brothers in building their famous aircraft, which accomplished the first manned, powered flight in 1903. It was likely due to this help that they accomplished their goal just ahead of the next closest contender, Samuel Pierpont Langley.
