The Field of Fluid Mechanics

Fluid mechanics extends the ideas developed in mechanics and thermodynamics to the study of motion and equilibrium of fluids, namely of liquids and gases.

The beginner in the study of fluid mechanics may have some intuitive notion as to the nature of a fluid, a notion that centers around the idea of a fluid not having a fixed shape. This idea indicates at once that the field of fluid mechanics is more complex than that of solid mechanics. Fluid mechanics has to deal with the mechanics of bodies that continuously change their shape, or deform. Similarly, the ideas developed in classical equilibrium thermodynamics have to be extended to allow for the additional complexity of properties which vary continuously with space and time, normally encountered in fluid mechanics.

Fluid mechanics bases its description of a fluid on the concept of a continuum, with properties which have to be understood in a certain manner. So far, neither the idea of a continuum nor that of a fluid have been properly defined. We, therefore, begin with the explanation of what a continuum is and how local properties are defined. We then describe the various forces that act in a continuum leading to the definition of the concept of stress at a point. The concepts of stress and continuum are then used to define a fluid.