Civil Engineering ⇒ Topic : Properties of Fluids
|1. Density or Mass Density : Density or mass density of a fluid is defined as the ratio of the
mass of a fluid to its volume. Thus mass per unit volume of a fluid is called density. It is denoted by the
symbol p (rho). The unit of mass density in SI unit is kg per cubic metre, i.e., kg/m3. The density of
liquids may be considered as constant while that of gases changes with the variation of pressure and
Mathematically, mass density is written as
2. Specific Weight or Weight Density : Specific weight or weight density of a fluid is the ratio between the weight of a fluid to its volume. Thus weight per unit volume of a fluid is called weight density and it is denoted by the symbol w.
w = ρg (∴ρ=Mass of fluid/Volume of fluid)
The value of specific weight or weight density (w) for water is 9.81 x 1000 Newton/m3 in SI units.
3. Specific Volume : Specific volume of a fluid is defined as the volume of a fluid occupied by a unit mass or volume per unit mass of a fluid is called specific volume. Mathematically, it is expressed as
4. Specific Gravity : Specific gravity is defined as the ratio of the weight density (or density) of a fluid to the weight density (or density) of a standard fluid. For liquids, the standard fluid is taken water and for gases, the standard fluid is taken air. Specific gravity is also called relative density. It is dimensionless quantity and is denoted by the symbol S.
= S x 1000 x 9.81 N/m3
The density of a liquid = S x Density of water
= S x 1000 kg/m3.
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