ABSTRACT
This chapter provides a brief review of some essential principles of physics, thermodynamics, and fluid mechanics. A relationship derived from either fluid dynamics or thermodynamics of importance to air sampling is Bernoulli's Equation, a derivation from the concept of energy conservation or momentum change. Fluid pressure measurement is nearly always made relative to the surroundings or atmospheric pressure by a mercury or water manometer, or by a pressure transducer or mechanical gauge. Such relative pressure is "gage" pressure and is positive if higher than surroundings, negative if lower. At the pressures and temperatures encountered in ambient air and exhaust gas measurement, the deviations are very slight, and little error is introduced in assuming ideal gas behavior. Both Boyle's and Charles' Laws are often employed together in air sampling to find the equivalent volume of an ideal gas at a temperature and pressure different from actual.
