1.
Density or Mass Density – Density or mass density of a fluid is defined as the ratio
of the mass of a fluid is defined as the ratio of the mass of a fluid to its
volume. Thus per unit of mass per unit of volume of a fluid is called density.
It is denoted by the symbol ρ (rho).
The unit off mass density in SI Unit is kg per cubic meter kg/m³.
|
ρ= mass of fluid/volume of fluid |
Note - The value of density of water is 1gm/cm³ or 1000kg/m³
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 small w.
w = weight of fluid /volume of fluid
w = (mass of fluid) Χ (acceleration due to gravity /volume of fluid) w = (mass of fluid) Χ g /volume of fluid [Mass of fluid /Volume of fluid =ρ]
|
w = ρg |
Note – The value of specific weight or weight density (w) for water is
9.81Χ1000 N/m³
3.
Specific
Gravity – Specific gravity is define as the
ratio of the weight density of a fluid to the weight density of a standard
fluid. For liquids, the standard fluid is taken water and gases, the standard
fluid is taken air. Specific gravity is also called relative density. It is
dimensional quantity and is denoted by the symbol S.
S(for
liquid) = weight density of
liquid/weight density of water
S(for
gases) = weight density of gas/weight density of air
Thus
weight density of liquid = S Χ weight density of water
= S Χ 1000 Χ 9.81 N/m³
The
density of liquid = S Χ density of
water
= S Χ
1000 kg/m³
If the specific
gravity of a fluid is known, then the density of the fluid will be equal to
specific gravity of fluid multiplied by the density of water.
For example - the specific gravity of mercury is 13.6,
hence density of mercury =13.6 Χ 1000 =
13600 kg/m³
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