TABLE OF CONTENTS Fluid mechanics is the study of fluids at rest or in motion. The topic is generally divided into two categories: liquids and gases. Liquids are considered to be incompressible, and gases are compressible. The treatment of incompressible fluids and compressible fluids each have their own groups of equations. However, there are times when a gas may be treated as incompressible (or at least uncompressed). For example, the flow of air through a heating duct is one such case. This chapter will concentrate on incompressible fluids.
Thermodynamic properties are important in incompressible fluid mechanics. Those of particular importance are density, specific gravity, specific weight, viscosity and pressure. Temperature is also important but is primarily used in finding other properties such as density and viscosity in tables or graphs.
The density, ?, is the mass per unit volume and is the reciprocal of the specific volume, a property used in thermodynamics:
The specific gravity, SG, is defined by the following equation
where 1000 kg/m 3 is the density of water at 4 C.
In many cases the specific gravity of a liquid is known or found from tables and must be converted to density using this equation.
The specific weight, ?, of a fluid is its weight per unit volume and is related to the density as follows:
where g = local acceleration of gravity, 
, and g c = gravitational constant:
The density...
