We explain what density is and some characteristics of this property. Also, other types of density that exist.

Gases have a lower density than liquids and solids.

What is density?

The term "density" comes from the field of physical and the chemistry and refers to the relationship that exists between the mass of a substance (or a body) and its volume. It is an intrinsic property of the matter, since it does not depend on the amount of substance that is considered.

Density, a property that is usually expressed in kilogram per cubic meter (kg / m3) or gram per cubic centimeter (g / cm3), varies to a greater or lesser extent depending on the Pressure and the temperature, and also with changes of state.

Due to the little cohesion between their particles, generally, gases have lower density than liquids and liquids have lower density than liquids solid.

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

During an immersion bath, Archimedes realized that he could calculate the volume of the corona by immersing it in Water and measuring the displacement of liquid, without having to melt or break it, and knowing the density of the gold (which is a constant) he could then weigh the crown and determine (using the formula) whether it was pure gold or an alloy (the density of gold would have varied when mixed with other metals).

Although there are exceptions, generally increasing the temperature decreases the density.

Density can be defined in several ways:

  • Density or absolute density. It is the relationship between the mass and the volume of a substance, be it solid, liquid or gaseous. It is represented by the Greek letter rho (𝞺):
    Where m is the mass of a substance and V is its volume.
  • Relative density. It is the relationship between the density of a substance and the density of another substance.
    Where 𝞺(substance X) is the density of the substance X and 𝞺 (substance Y) is the density of the substance Y, with respect to which the relative density of X.
  • Apparent density. It applies to porous materials, which may have air or other substances incorporated between their pores. It is calculated in a similar way to density, but you have to add the mass of air of the substance that occupies the pores. It is also necessary to increase the volume of the substance, incorporating the volume occupied by the substance that occupies the pores.
    The density of water is 1 g / cm3 and that of lead it is 11.35 g / cm3. In these two examples we can see how the density can take very different values ​​at different materials.

Other types of density

Low bone mineral density can trigger osteoporosis.

  • Population density. It is a concept demographic which refers to the number of inhabitants per square kilometer. China and India are examples of countries with very high population density, while the Nordic and Oceania they have low population density. High population density areas are often associated with housing problems, air pollution, insufficient infrastructure public services, among others.
  • Optical density. It is a physical parameter that constitutes the absorption of an optical element at a length given wave per unit distance. This data is used to assess the content of cells, quality of fumes generated by different substances, power of a laser, filters, etc.
  • Electric current density. It is the relationship that exists between the intensity of electric current that circulates through a conductor per unit of weather and per unit of cross section.
  • Magnetic flux density. Also called "magnetic induction", it is the magnetic flux that causes an electric charge on movement for each unit of area normal to the direction of flow.
  • Bone mineral density. In the medical field, this measure refers to the amount of minerals per unit area. It is usually expressed in g / cm2 and is established for certain bones specifically, such as the femur or the lumbar spine. Low bone mineral density can trigger osteoporosis, a disease in which the bones are very low proportion minerals (mainly calcium), so they become too porous and, therefore, brittle and brittle, thus increasing the risk of the persons to suffer fractures.

Examples of the density of some compounds and elements at 20 ° C

  • Magnesium (Mg). 1,738 g / cm3
  • Calcium (Ca). 1.54 g / cm3
  • Iron (Fe). 7.874 g / cm3
  • Molybdenum (Mo). 10.22 g / cm3
  • Silver (Ag). 10.5 g / cm3
  • Gold (Au). 19.3 g / cm3
  • Water (H2O). 1 g / cm3
  • Oil 0.92 g / cm3
  • Air. 1,225 x 10-3 g / cm3
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