Density is defined as the mass per unit volume of a material. The symbol used to represent density is ρ (the lower case Greek letter rho). Density is defined as mass divided by volume, mathematically:
Density (ρ) = Mass (m)
Where ρ is the density, m is the mass, and V is the volume. The SI unit for density is kilograms per cubic meter (kg/m3).
Fluids that are less dense float on more dense fluids if they are put together. This can also be applied to less dense solids floating on more dense fluids. If the average density of on object is less than that of water it will float in water, but if it’s denser than water it will sink.