**DENSITY (Kg/m^3 or** N•sec²/m^4 **)**

Density is defined as **mass per unit volume** . Mass is a property.

Density can be expressed as

*ρ = m / V*

**SPECIFIC VOLUME (m^3/kg or** m^4/ N•sec² **)**

Specific volume on the other hand is the reciprocal of density.

Specific volume = 1/ density

**SPECIFIC WEIGHT (** N/m³ or lb/ft³ or kg/m²•sec²)

Specific Weight is defined as weight per unit volume. Weight is a **force** .

*γ = ρ g*

**SPECIFIC GRAVITY /RELATIVE DENSITY (Dimensionless)**

For liquids defined as the ratio of the density of a substance to the density of water - at a specified temperature.

*SG = ρsubstance / ρH2O*

The reference density of water at 4oC (39oF) is used as the reference as these are the conditions of maximum density.

*For gases*

*SG = Mass of gas / Mass of air =* *Mass of gas / 28.97*