What is the Density of Matter?

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What Does Density of matter Mean

Density is a scalar quantity , often used in physics and chemistry , which refers to the amount of mass present in a given body or substance per unit volume. It is usually represented by the symbol ρ.

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Two bodies or substances of the exact same size and proportions can have different densities , and this is measured through the average density, which is the relationship between the mass of a body and the volume it occupies in space, according to the following formula:

where m is mass and V is volume , so the unit of measurement for density in the International System will be the kilogram per cubic meter (kg / m 3 ) or equivalent units of measurement.

Variations in temperature and pressure affect the measurement of the density of a substance.

The density of matter is often associated with the story of the Greek philosopher Archimedes , who was supposedly tasked with determining whether the king's crown had been forged using pure gold or whether it had been made from an alloy with other metals .

During an immersion bath, Archimedes realized that he could calculate the volume of the crown by immersing it in water and measuring the displacement of the liquid , without having to melt or break it. Then he could weigh the crown (to have its mass) and determine, using the formula detailed above, the density of the crown. He compared the values ​​of the calculated density of the crown with the density of pure gold (which is a constant), and this way he knew if it was pure gold or an alloy, since the density of gold would have changed when mixed with other metals.

See also: Specific gravity

Density types

There are several types of density of matter:

  • Absolute density. Usually we speak of absolute density when we use the term density , and it is an intensive quantity calculated, as we said above, from volume and mass. Its SI units of measurement are (kg / m 3 ).
  • Relative density. This other type, on the other hand, arises from the comparison between the density of the substance in question and some other that serves as a reference, so it is a dimensionless quantity (without units). For liquids and solids , the density of water is used as a reference (at 1atm and 4 ° C), while for gases the density of air is used (at 1atm and 0 ° C). It is calculated as follows:

    where r is the relative density, is the absolute density and 0 is the density of the reference substance.
  • Apparent density. It is applied to heterogeneous materials, as well as to porous ones, whose mixture affects the density (being less than if each element were compacted separately). Hence, this type of density does not depend on the nature of the matter, but on the way it is arranged. For example, if we have a hydrated material, its apparent density will be:

    where
    a is the apparent density of the material, mh is the mass of the dried material and V0 is the volume of the hydrated material, that is, without drying.

Examples of density

Some examples of the absolute density of different elements and substances (expressed in their appropriate units) can be:

  • Magnesium (Mg). 1,738 g / cm 3
  • Calcium (Ca). 1.54 g / cm 3
  • Iron (Fe). 7.874 g / cm 3
  • Molybdenum (Mo). 10.22 g / cm 3
  • Silver (Ag). 10.5 g / cm 3
  • Gold (Au). 19.3 g / cm 3
  • Iridium (Go). 22.562 g / cm 3
  • Dubnio (Db). 29.3 g / cm 3
  • Bohrio (Bh). 37.1 g / cm 3
  • Water (H2O). 1 g / cm 3
  • Oil. 0.92 g / cm 3
  • Air . 1,225 kg / m 3
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