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RELATIONSHIP TO CONTINUUM MECHANICS


Fluid mechanics is often considered a subdiscipline of Continuum Mechanics , as illustrated in the following table.



THE CONTINUUM ASSUMPTION


Fluids are composed of Molecules that collide with one another and solid objects. The continuum assumption, however, considers fluids to be Continuous . That is, properties such as density, pressure, temperature, and velocity are taken to be well-defined at infinitely small points, and are assumed to vary continuously from one point to another. The discrete, molecular nature of a fluid is ignored.

Those problems for which the continuum assumption does not allow solutions of desired accuracy are solved using Statistical Mechanics . To determine whether or not to use conventional fluid dynamics (a subdiscipline of Continuum Mechanics ) or statistical mechanics, the Knudsen Number is evaluated for the problem. Problems with Knudsen numbers at or above unity should be evaluated using statistical mechanics for reliable solutions.


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