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# Define the term relative density of a substance.

Last updated date: 21st Jul 2024
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Hint: Before going to the question let us first have a brief idea of specific gravity. Specific gravity or relative density is a dimensionless quantity that is defined as the ratio of the density of a substance to the density of water at a specified temperature and pressure.

Complete step by step answer:
The ratio of a substance's density to the density of a given reference material is known as relative density or specific gravity. For liquids, specific gravity is almost always determined in relation to the densest water; for gases, the reference is air at room temperature.
The density of a sample can be directly determined by dividing it by the density of the reference material (which is known). The sample's density is equal to its mass divided by its volume.
$RD = \dfrac{{{\rho _{substance}}}}{{{\rho _{reference}}}}$
Where,
$RD$ = Relative density
${\rho _{substance}}$ = Density of the substance being measured.
${\rho _{reference}}$= Density of the reference.

Additional information: A material's relative density is less than one if it is less dense than the comparison, and greater than one if it is denser. If the relative density is exactly one, the densities are equal; that is, equal volumes of the two substances have the same mass. If the reference material is water, a substance with a relative density (or specific gravity) less than 1 will float in water. For example, an ice cube with a relative density of 0.91 will float. If the relative density of a substance is greater than one, it sinks.

Note: Relative density can also be used to calculate a substance's buoyancy in a fluid or gas, or to measure the density of an unknown substance based on the density of a known substance. Geologists and mineralogists also use relative density to calculate the mineral content of a rock or other sample. It is used by gemologists to help in the identification of gemstones. Water is preferred as a reference because field measurements are easier to perform.