Fluid is a subtance (liquid or gas) which can deform continously under the action of shear stress.

There are 2 types of fluid:

Ideal Fluid: which does not have surface tension, viscosity and are incompressible.

Real Fluid: Fluids that are not Ideal.

In reality Ideal Fluid does not exist.

$Density,\rho =\frac{mass}{Volume}$

$G=\frac{\rho }{{\rho}_{Standard}}$

$\gamma =\rho g$

$K=-\frac{dP}{{dV}/{V}\;}=\frac{dP}{{d\rho }/{\rho }}$

$\tau =\mu \frac{du}{dy}$

$\upsilon =\frac{\mu }{\rho }$

${{\mu }_{liq}}=a{{10}^{\left( \frac{b}{T-c} \right)}}$

${{\mu }_{gas}}=\frac{a\sqrt{T}}{1+{}^{b}/{}_{T}}$

$\Delta {{P}_{1}}=\frac{2\sigma }{r}$

$\Delta {{P}_{2}}=\frac{4\sigma }{r}$

$\Delta {{P}_{3}}=\frac{2\sigma }{d}$

$h=\frac{4\sigma \cos \theta }{\gamma d}$

$G=$ Spective Gravity or Relative Density of Fluid
${{\rho}_{Standard}}=$ Density of some standard fluid at standard temperature (usually water at $4{}^\circ C$)
$\gamma =$ Specific Weight or weight density of liquid
$g=$ Acceleration due to gravity
$K=$ Bulk Modulus
$dP=$ Increase in Pressure
${{dV}/{V}}=$ Chnage in Volume per unit Volume
$\tau =$ Shear Stress
$\mu =$ Dynamic Viscosity
$\frac{du}{dy}=$ Velocity Gradient
$\upsilon =$ Kinematic Viscosity
${{\mu }_{liq}}=$ Dynamic viscosity of liquid
${{\mu }_{gas}}=$ Dynamic viscosity of gas
$\sigma=$ Surface Tension

General relationship between shear stress and velocity gradient is,

Types of Fluids	Examples
Dilatant	Suspended Starch or sand, sugar in water, butter
Newtonian	Water, air, alcohol
Pseudo Plastic	Paints, polymer solutions, blood, paper pulp, syrup, milk
Rheopectic	Gypsum, lubricants
Bingham Plastic	Tooth Paste, Sewage sludge, drilling mud
Thixotropic	Printer's Ink, Ketchup, enamels