(1) The mass per unit volume of a substance is called the "density" of this substance. Density is the ratio of the mass m of a substance to its volume v, which is defined as
ρ=m/V
According to the definition, in the international system of units, the unit is kilograms per cubic meter (kg/m3) and the dimension is ML-3.
(2) Apparent density
The ratio of the mass of porous solid (particle or powder) material to its apparent volume (including pore volume).
(3) Actual density
The ratio of porous solid material to its static volume (excluding pore volume).
(4) Bulk density
Under certain conditions, in a container with a given volume, the ratio of the mass of loose materials (chips, particles, fibers) to the volume occupied.
Specific conditions refer to natural accumulation, vibration or knocking or accumulation under a certain pressure.
(5) Standard density
Density of substances under standard conditions specified in the specification. For example, the standard density of gas at a temperature of 273. 15K(0℃) and a pressure of 10 1325Pa(latm); Standard density (latm) of liquid at 20℃ temperature and pressure.
(6) Reference density
The density of a substance at a specific reference state (temperature and pressure).
(7) Relative density
Under some conditions, the ratio of material density ρ 1 to reference material density ρ2 is defined as
d=ρ 1/ρ2 .
Relative density used to be called "specific gravity". "Specific gravity" usually refers to the ratio of the density of a substance to the density of pure water, which has been included in the above concept of relative density. There is another definition of "specific gravity" in history, that is, the weight per unit volume, which shows that the concept of "specific gravity" itself is rather confusing and is no longer used.
Density is an important physical quantity to characterize the characteristics of matter. Moreover, the mass per unit volume of the same substance is a fixed value, and the mass per unit volume of different substances is different. Therefore, the mass per unit volume can be used to characterize this characteristic of matter.