Density
Density is a measure of mass per volume. This use of density is also known (if you follow ISO 31) as volumic mass. The higher density, the higher mass per volume.
In the SI system on units, density is measured as kg m-3 (kilograms per cubic metre), but many people use the more convenient g cm-3 (grams per cubic centimetre) or (equivalently) kg l-1 (kilograms per litre).
- 1000 kg/m3 = 1 g/cm3 = 1 kg/l.
Formerly mass and volume were linked by defining the gram to be the mass of one cubic centimetre of water at 4°C which meant that water had density 1 kg/litre. However, using one cubic centimeter of water as a standard for one gram is problematic due to the possibility of mass loss from evaporation as well as changes in density with temperature. For this reason alternate definitions of the metre and kilogram have been developed, which can be reproduced more reliably in a laboratory. Because of slight changes in the metre and kilogram due to these new definitions, the density of water at 4°C is not quite exactly 1, but 0.99995 kg/litre. A cubic metre of water thus weighs approximately one metric ton.
Perhaps the highest density known is reached in neutron star matter. The singularity at the centre of a black hole, according to general relativity, does not have any volume, so its density would be be seen as either infinite or non-existent.
The densest naturally occurring substance on Earth is osmium, its density is about 22 kg/litre.
Relative Density
Relative density is a dimensionless quantity defined as the density of a substance divided by the density of water at standard temperature and pressure. By definition, then, the relative density (or RD) of water is 1, and the RD of osmium is about 22.
External link
Conversion Calculator for Units of DENSITY
Density may denote how much of a certain substance, object or occurrence is present within a certain area or volume. Often used is population density, meaning how many people on average live in an area (usually persons per square kilometre).