Viscosity is defined as the property of a fluid which offers resistance of the movement of one layer to of fluid over another adjacent layer of the fluid.When two layers of the fluid, a distance 'dy' apart, move one over the other at different velocities, say u and u + du , the Viscosity together with relative velocity causes a shear stress acting between the fluid layers. CLICK HERE

unit of Viscosity

            The unit of Viscosity is obtained by putting the dimensions of the quantities in above equation.SI unit of Viscosity is N s/m^2 or Pa.s. Again it can be also expressed in MKS unit as Poise.  CLICK HERE

1 N s/m^2 = 10 Poise

             It is defined as the ratio between the Dynamic Viscosity and Density of fluid.It is denoted by symbol  ν (nu).  CLICK HERE

Mathematically, ν = μ/ρ 

            By putting on above equation we get SI unit of Kinematic Viscosity is m^2/s.Again as Dynamic Viscosity it can be also expressed in MKS unit in Stokes.

1 cm^2/s = 1 Stokes

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          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.   CLICK HERE

It is dimensionless quantity and is denoted by symbol S. 

Mathematically, S (for liquids) = Density of liquid / Density of water 

                     S (for gases) = Density of gas / Density of air

The weight density of a liquid = S x Weight density of water

                                             = S x 1000 x 9.81 N/m^3

             The density of a liquid= S x 1000 kg/m^3    CLICK HERE 

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 the Density of mercury = 13.6 x 1000 = 13600 kg/m^3. CLICK HERE

          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.   CLICK HERE

Mathematically, Specific Volume = volume of fluid / mass of fluid 

                        = 1 / Density

       

The  Specific volume is the reciprocal of mass density. CLICK HERE

It is expressed as m^3/kg .It is commonly applied to gases.
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               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  Specific weight and it is denoted by w.

Thus mathematically, w = weight of fluid / volume of fluid 

                                                                                              = (mass of fluid x acceleration due to gravity) / volume of fluid

      = Density x g

Therefore, w = ρ g

what is Density or Mass Density?