 
Summary: 1
Molecular vs. Continuum
·
Classical fluid mechanics (i.e., A&AE 511) treats a gas as an
infinitely divisible substance, a continuum.
·
As a consequence of continuum assumption, each fluid property
is assumed to have a definite value at each point in space.
Density, temperature, velocity, and so on, are considered to be
functions of position and time.
·
For most of gas dynamics phenomena experienced by humans (1
atm pressure, room temperature, length scales ~ 1 m), continuum
hypothesis is valid.
·
However, many modern engineering applications (space flight,
microelectromechanical devices) occur at conditions where
more detailed molecular description of the structure of gaseous
matter is necessary.
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