MrsDrPoe: Physical Characteristics of Fluids

Good morning all! Today we'll be defining certain fluid properties that are key to fully understanding fluid dynamics.

density - mass of fluid per unit volume of fluid; liquids are typically much more dense than gasses; in liquids changes in pressure and temperature have little effect on density; in gasses changes in density are related to changes in pressure and temperature through the ideal gas law

specific volume - volume of fluid per unit mass; the inverse of density

specific weight - weight (mass x gravitational constant) of fluid per unit volume of fluid; equal to density x gravitational constant

specific gravity - ratio of density of a given fluid to the density of water at 39.2 degrees Farenheit

viscosity - (also absolute viscosity or dynamic viscosity) resistance of fluid to flow; fluid friction

kinematic viscosity - ratio of viscosity to density

bulk modulus - describes the compressibility of a fluid; fluids with large bulk modulus are considered incompressible (no more mass of this fluid could be forced in a given volume, i.e. the density of the fluid is constant)


These fluid properties that are dependent on the amount of mass present (mass, volume, energy) are called extensive properties; those that are independent of the amount of mass (density, viscosity, temperature, pressure) are known as intensive properties.