04/19/2020
PROPERTIES OF FLUID
Before studying Fluid mechanics, we have to have basic idea of following properties of fluid. Some properties may rely on other ones.
Density
Density is a measure of mass per unit volume. At a point density can be expressed as follow
ρ=lim┬(δV→0)〖δm/δV 〗
ρ -Density
m-Mass
V-Volume
When considering an volume it has completely filled with same fluid (material) Density can be expressed as follow.
ρ =〖m/V 〗
Dimension of density - [M][〖L]〗^(-3)
SI Unit of density - kgm^(-3) ,
Other Units of density which are generally used - lb〖ft〗^(-3) ,gcm^(-3)
Specific weight (Unit density) - γ
Specific weight is the measure of weight per unit volume can be expressed as follow.
γ =〖mg/V 〗 g -accelaration due to the gravity
Hence there is a direct relation between density and specific weight.
γ =〖ρg 〗
Dimension of Specific weight = [M][〖L]〗^(-3) × [L] 〖[T]〗^(-2)
=[M][〖L]〗^(-2) [T]^(-2)
SI Unit – Nm^(-3)
Relative Density (Specific Gravity) - S
Relative Density of a substance =〖(Density of the substance )/(Density of the standard substance) 〗
Water is generally used as the standard substance. This is a dimensionless and unitless property.
Pressure – P
Due to the collision of molecules, FluidS exert force on surfaces which are in contact with them. This Force per unit contacted area can be defined as pressure.
Pressure(P)=〖(Force (F))/(Area (A)) 〗
At a point, it can be expressed as follow.
P=lim┬(δA→0)〖δF/δA 〗
Dimension of Pressure – [M][〖L]〗^(-1) [T]^(-2)
SI units of pressure – Nm-2
