Difference Between Density and Relative Density (With Table)

Density and relative density are two concepts that help determine the volume and mass of a substance. Although the two may seem similar concepts, they are different. The symbol, SI unit, measurement, and other names of density and relative density vary from each other.

Density vs Relative Density

The difference between density and relative density is that density measures the mass per unit volume. In contrast, relative density measures the mass per unit volume by given reference material. Density is specific to each substance. On the other hand, the relative density of a substance varies in accordance with the given reference material. 

The density of certain common solids, liquids, and gases are a part of every science textbook. The symbol of density is ρ, which is the lowercase Greek letter rho. Density usually depends on the volume of a body. In addition, an increase in pressure causes a decrease in the density of an object by increasing its volume. The formula for mass is M=Vd, and the formula for volume is V=M/d. Density provides a convenient way to measure the mass and volume of a substance.

The relative density of a substance indicates if the material will float or sink. If the relative density of a material is less than 1, it is less dense than the reference material. However, if it is more than 1, then the substance is denser than the reference material. The factors that influence relative density are temperature, pressure, and the nature of the material.

Comparison Table Between Density and Relative Density

Parameters of ComparisonDensityRelative Density
SymbolThe symbol of density is ρ. The symbol of relative density is SG. 
Another NameAnother name of density is specific weight. Another name of relative density is specific gravity.
MeaningDensity measures the mass per unit volume. Density provides a convenient way to measure the mass and volume of a substance. Relative density measures the mass per unit volume in accordance with a given reference material. 
SI unitThe SI unit of relative density is kg/m3.Relative density has no SI unit. 
MeasurementDensity is specific to each substance. Different materials have varying densities. The densest known elements at room temperature are osmium and iridium.Relative density of a substance varies in accordance with the given reference material. 

What is Density?

Density refers to mass per unit volume. The formula for the same is d=M/V, where M is the mass and V is the volume. At most times, density is expressed in gram per cubic centimetre or kilogram per cubic centimetre. Consider, for example, the density of Earth, which is 5.51 grams per cubic centimetre. Another example is the density of air that is 1.2 kilograms per cubic meter. 

Density provides a convenient way to measure the mass and volume of a substance. The formula for mass is M=Vd, and the formula for volume is V=M/d. The density of certain common solids, liquids, and gases are a part of every science textbook. The symbol of density is ρ, which is the lowercase Greek letter rho. 

The density and mass concentration of a pure substance is the same. However, different materials have varying densities. The densest known elements at room temperature are osmium and iridium. The density of substances varies following pressure and temperature. This variation is the most prominent for gases, followed by liquids and solids.

Density usually depends on the volume of a body. In addition, an increase in pressure causes a decrease in the density of an object by increasing its volume. However, there are some exceptions. In conclusion, the density of any substance is determined by its temperature, electric field, physical state, composition, allotropic shape, etc. 

What is Relative Density?

Relative density refers to the mass per unit volume of a substance concerning a specific given material. Another name of relative density is specific density. At most times, the relative density of liquids calculates concerning water as the reference material. In contrast, the reference material taken into account for gases is air.

If the relative density is less than 1, it is less dense than the reference material. However, if it is more than 1, then the substance is denser than the reference material. If the relative density is equal to 1, then the material and the reference material have equal densities. Relative density has no SI unit. 

The symbol denoting relative density is SG. The relative density of a substance indicates if the material will float or sink. The relative density of rubbing oil is 0.79gram/cm3, the density of water is 1gram/cm3. Relative density is a physical quantity with no specific dimensions. Different substances have different relative densities. 

The factors that influence relative density are temperature, pressure, and the nature of the substance. Different ways to calculate relative density are hydrometer, Pycnometer method, oscillating densitometer, buoyancy method, immersed body method, and hydrostatic method. In conclusion, relative density measures density concerning a given material. 

Main Differences Between Density and Relative Density

  1. Another name of density is specific weight. On the other hand, another name of relative density is specific gravity.
  2. The symbol of density is ρ. In contrast, the symbol of relative density is SG. 
  3. The SI unit of relative density is kg/m3. However, relative density has no SI unit.
  4. Density measures the mass per unit volume. In contrast, relative density measures the mass per unit volume following a given reference material. 
  5. Density is specific to each substance. On the other hand, the relative density of a substance varies in accordance with the given reference material. 

Conclusion

The difference in the meaning, SI unit, measurement, other names, and symbol of density and relative density justify the claim that the two are different concepts. The symbol of density is ρ. In contrast, the symbol of relative density is SG. The factors that influence the density of a material is its temperature, electric field, physical state, composition, allotropic shape, etc. 

The density and mass concentration of a pure substance is the same. However, different materials have varying densities. In contrast, relative density is a physical quantity with no specific dimensions. Different materials have different relative densities. Another name of density is specific weight. On the other hand, another name of relative density is specific gravity.

References

  1. https://ascelibrary.org/doi/abs/10.1061/JSFEAQ.0001642 
  2. https://ascelibrary.org/doi/abs/10.1061/AJGEB6.0000521 
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