Density

The density (noted ρ rho ) is a characteristic of material. It is the report/ratio \ rho = \ textstyle \ frac {m} {V} of the Masse m of a homogeneous substance, corresponding to a Volume V of this substance and independent of the selected quantity.

However the volume of a given mass varies according to several parameters. It depends in particular on the temperature and, particularly for gases, on the pressure. Certain materials (whose wood) which can absorb water, moisture modifies also the density. For the porous grounds and materials, it is also necessary to take account of the weight of the air contained in volumes of the vacuums, but in practice, they are often neglected.

Measuring units

The measuring unit of the density is the kilogram per cubic meter (kg.m -3 or kg/m 3 ). It is a Unité derived from the international system.

The density is sometimes expressed in g/cm 3 , kg/dm 3

Note:

  1. In these units, the numerical value does not change because 1 g/cm 3 = 1 kg/dm 3 = 1 t/m 3 .
  2. the ton is not a unit of mass of the international Système. It is advisable to use the Kilogram and its multiples or submultiples.
  3. the density of water is close to 1 kg/dm 3 . It is not a chance, but that results from the first attempts at definition of the kilogram: mass of one liter water (one decimetre cubic). (Its actual value is, to 4 °C, of 999,95 kg/m 3 ).

Density and density

See also: Density

The Densité of a material is, for the solid S and the Liquide S, the report/ratio of the density of this material to that of the Eau. For the Gas, the density is calculated in connection with the density of the air. In both cases, the density is thus a number without dimension (thus without unit).

Tables of the densities of various substances

Unless otherwise specified, the densities are given for bodies to the temperature of 20 °C , under the Atmospheric pressure normal.

Particular case of wood

Wood is a living matter whose density varies mainly according to two parameters: gasoline and moisture.

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