Density and Specific Gravity

Specific gravity is calculated by dividing the density of a substance by the density of a standard or reference substance. Water is commonly used as a standard of comparison. Density, on the other hand, is measured in terms of weight units in relation to the size of the object. Density is calculated by dividing the mass by the volume of the object. It is the measurement of density in relation to the density of pure water that is referred to as specific gravity, also known as relative density.

Density

The density of a substance is defined as the mass per unit volume of the substance. The symbol for density most commonly used is ρ  (the lowercase Greek letter rho), although the Latin letter D can also be used to represent the quantity. Density is defined mathematically as the product of mass divided by volume:

ρ = m/V

 Where ρ  denotes the density, and

The mass is represented by the letter m.

The letter V stands for volume.

The density of a material changes in response to changes in temperature and pressure. Solids and liquids typically exhibit only minor variations, whereas gas exhibits significantly greater variations. Increasing the pressure applied to an object causes the object’s volume to shrink, resulting in an increase in its density. With a few exceptions, raising the temperature of a substance causes its density to decrease by increasing the volume of the substance. Increasing the heat convection from the bottom to the top of a fluid in most materials occurs due to the decreased density of the heated fluid, which causes it to rise in comparison to the denser unheated material in most materials.

Specific Gravity

When a substance has a density greater than or equal to that of water at a specified temperature, it is said to have Specific gravity, which is a dimensionless quantity defined as the ratio of the density of the substance to the density of water at that temperature and is expressed as

Specific gravity, S= ρsubstsnce / ρwater

Here, ρsubstsnce = Density of the substance being measured

ρwater  =  Density of the reference

It is common practice to use the density of water at 4oC as a reference point because water at this temperature has the highest density of 1000 kg/m3, making it an excellent reference point.

Specific gravity is defined as the ratio of the density of a substance or liquid to the density of water at a given temperature and pressure under certain conditions. Therefore, any change in temperature or pressure will have an effect on the density of a substance.

Difference Between Density and Specific Gravity

• Density is defined as the mass of an object per unit volume, whereas relative density, also known as specific gravity, is defined as the ratio of a substance’s weight to the weight of the same volume of water. Density and specific gravity are two different concepts.
• The density of a substance can be calculated by knowing its weight and volume, whereas the specific gravity of a substance can be calculated by dividing the density of a substance by the density of water.
• When it comes to density, the absolute value is used, whereas specific gravity is represented in the relative value.
• Specific gravity, on the other hand, does not have a SI unit and for density it is represented in kilograms per cubic metre. The symbol for density is and is represented in kilograms per cubic metre.
• When it comes to domestic and commercial applications, density is frequently used; however, specific gravity is more commonly encountered when measuring the concentration of solutions in industrial settings.

Specific gravity values of a substance are not commonly encountered in everyday life. It is, on the other hand, extremely useful in predicting whether or not something will float when submerged in water. Another application is to determine whether one substance is denser than another by comparing their densities. Pure water has a density of approximately 1 gram per cubic centimetre and is transparent. As a result, specific gravity and density are nearly equal in magnitude and proportion. In reality, density is only a fraction of a percent less than the specific gravity number.

Density and specific gravity are never the same because density has units and specific gravity is dimensionless. However, when three conditions are met, the two are numerically equal:

Density is measured in grams per cubic centimetre, grammes per millilitre, or kilogrammes per litre, depending on the unit of measurement.

When measured at the same temperature, density and specific gravity are the same.

The Specific Gravity is calculated using water at 4 degrees Celsius, where its Density is very close to 1 gramme per cubic centimetre and its Specific Gravity is 0. It is possible to calculate the density of a material by multiplying the Specific Gravity by the Density of water at the reference temperature.

How to Calculate Density and Specific Gravity

Specific gravity numbers aren’t very useful for anything other than predicting whether or not something will float on water and comparing whether one substance is more or less dense than another. However, because the density of pure water is so close to one (0.9976 grams per cubic centimetre), the specific gravity and density of pure water are nearly identical when expressed in grams per cubic centimetre (g/cc). Specific gravity is less dense than density, by a small margin.

Conclusion

Density and specific gravity are both measures of mass that can be used to compare different types of substances. They are not, however, the same measurements as one another. The specific gravity of a substance is an expression of its density in relation to the density of a reference standard (usually water). In addition, density is expressed in units (weight in relation to size), whereas specific gravity is expressed as a pure number or as a dimensionless quantity.