All objects have density, whether it’s a solid, liquid, or gas. However, having an understanding of what density is, is very important for fluid mechanics, since density is used in a majority of fluid mechanics calculations. So what is density. Density is the mass of a substance over a certain unit volume. Density is represented by the greek letter rho. Refer to equation 1.

**(Eq 1)** $ρ=\frac{m}{V}$

ρ = Density

m = mass

V = Volume

Specific volume on the other hand is the reciprocal of density. Refer to equation 2.

**(Eq 2)** $ν = \frac{1}{ρ}$

ν = Specific Volume

Finally, another aspect that is important to know for fluid mechanics is a fluid’s specific weight. Specific weight relates the fluid’s density and the effects of the gravitational constant. It is represented by the greek letter gamma. Refer to equation 3 to calculate specific weight.

**(Eq 3)** $γ=ρg$

γ = Specific Weight