| • Science | • People | • Locations | • Timeline |
| Contents | ||
Density (symbol: ρ - Greek: rho) is a measure of mass per unit of volume. The higher an object's density, the higher its mass per volume. The average density of an object equals its total mass divided by its total volume. A denser object (such as iron) will have less volume than an equal mass of some less dense substance (such as water).
The SI unit of density is the kilogram per cubic metre ( kg/ m3)
where
ρ is the object's density (measured in kilograms per cubic metre)
m is the object's total mass (measured in kilograms)
V is the object's total volume (measured in cubic metres)
Under specified conditions of temperature and pressure, density of a fluid is defined as described above. However, the density of a solid material can be different, depending on exactly how it is defined. Take sand for example. If you gently fill a container with sand, and divide the mass of sand by the container volume you get a value termed loose bulk density. If you took this same container and tapped on it repeatedly, allowing the sand to settle and pack together, and then calculate the results, you get a value termed tapped or packed bulk density. Tapped bulk density is always greater than or equal to loose bulk density. In both types of bulk density, some of the volume is taken up by the spaces between the grains of sand. If you are interested in the density of the grain of sand itself you need to measure either envelope density or absolute density.
Some people still use the old g/ cm3 (gram per cubic centimetre) or kg/ L (kilograms per litre) to measure density,
instead of the correct kg/ m3.
1000 kg/m3 = 1 kg/dm3 = kg/L or 1 g/cm3 = 1 g/mL.
In Imperial units or U.S. customary unit, the unit of density is the poundOfficially the pound is the name for at least three different units of mass: the pound (avoirdupois the troy pound the obsolete imperial pound There also exists an unofficial metric pound . While most standards bodies define the pound as a unit of mass, m/ cubic footThe cubic foot (symbols ft cu. is a nonmetric unit of volume, used in U. customary units and Imperial units. It is defined as the volume of a cube with edges one foot in length. 1 cubic foot is equal to: 1,728 cubic inches 0. 037037 (1/27) cubic yard 7..
Formerly mass and volume were linked by defining the gram to be the mass of one cubic centimetre of water at 3.98 °C which meant that water had density 1 kg/litre. However, using one cubic centimetre 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 alternative definitions of the meter and kilogram have been developed, which can be reproduced more reliably in a laboratory. Because of very slight changes in the metre and kilogram due to these new definitions, the density of clean water at 3.98 °C is very close to exactly 1 kg/litre. A cubic metre of water thus weighs one metric tonne.