Fluids are materials that can flow, and they include both gases and liquids. Air is the most common gas fluid and water is the most common liquid fluid. The density of a liquid or gas is one of the most important factors that determines its behavior as a fluid. Density is the mass per unit volume and is represented by the Greek letter rho (ρ).
ρ = mass / volume
The SI unit of density is kg/m3
In chemistry we usually stated that at 4ºC the density of water was 1.0 g/mL. In physics we use the SI unit for density mentioned above. What is the density of water in the proper SI units?
The density of blood is 1060 kg/m3. If a man's body weighs 690 N and contains about 5.2 x 10-3 m3 (5.5 qt) of blood, what percentage of the man's body weight is his blood?
A convenient way to compare densities is to use the concept of specific gravity. The specific gravity of a substance is its density divided by the density of a standard reference material, usually chosen to be water at 4ºC. Being the ratio of two densities, specific gravity has no units.