The physical properties of fluids are as follows:
1.3.1 Mass Density or Density
Mass density or simply density of a fluid is defined as the mass per unit volume. It is denoted as p (rho). If 6.m and Si are mass and volume respectively of a fluid element enclosing a point P, then p is mathematically written as
Fig. 1.1 shows a fluid element enclosing point P.
S.I. (Standard International) unit of p is given by
P water = 1000 kg / m3
1.3.2 Specific Weight or Weight Density
The specific weight or weight density of a fluid is defined as the weight of the fluid per unit volume. It is denoted as w. It is mathematically expressed as
w = gp or w = pg
where dW = weight of fluid element.
W water = 9.81 x 1000 N/m3
The volume of a fluid per unit mass is called specific volume. It is denoted as v. It is mathematically expressed as
u = 1 /p
In S.I unit it is m3 / kg. We encounter v frequently in case of gases only.
1.3.4 Specific Gravity
The specific gravity of a liquid is defined as the ratio of weight density or density of the liquid to the weight density or density of pure water at pressure 101 KN/m2 and temperature at 4°C. It is denoted as S. It is mathematically expressed as
S = w liquid / w std.water = w liduid / 9.81 x 1000 N/m3
or w liquid = S x 9.81 x 1000 N/m2
S can also be expressed as
S = p liquid / p std.water = p liduid / 1000 kg/m3
or p liquid = S x 1000 kg/m2