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• Specific gravity

Density is defined as the mass of a unit volume of some material. The term unit volume means the amount contained in one volumetric unit of measurement: one cubic foot, one liter, or one milliliter, for example. The density of pure iron, for instance, is 7.87 grams per cubic centimeter (7.87 g/cm³). That statement means that one cubic centimeter (1 cm³) of iron has a mass of 7.87 grams.

Density is an important measurement because it allows for the comparison of the heaviness of two materials. Rather than asking, "Which is heavier: iron or Styrofoam™?," the proper question to ask is: "Which is more dense: iron or Styrofoam™?" This question is more appropriate because it asks about a comparison between equal amounts of two different materials.

Specific gravity

Another form of measurement...