Specific Gravity

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Specific gravity is an essential chapter in Physics. It has several real-life implications and applications. For example, when young children start learning to swim, they use floaters. Similarly, when we travel on a boat, we expect the boat not to have any leaks. Several factors contribute to the floating of any object on any liquid. One such factor is specific gravity. We will learn about the particular gravity in detail in this chapter.


What is Specific Gravity?

If you want to understand physics properly, you must know what is specific gravity. It is also known as relative gravity. It does not have any dimension. It is the ratio of a substance’s density to that of water at a particular temperature. The temperature has a vital role in determining the specific gravity of any substance. Therefore, specific gravity is a property of the substance at a particular temperature. Pressure also affects the specific gravity of any substance.

According to the specific gravity definition, specific gravity can be expressed mathematically as

SG= ρsubstancewater

In general, the specific gravity of any substance is defined concerning water at 4⁰C. This temperature is considered because the water density at that temperature is 1000kg/m³ or 1g/cm³. The density of water in other units can also be used to calculate any substance's specific gravity value. The different densities of water are 62.43 pounds per cubic foot and 0.036 pounds per cubic inch.

Specific Gravity = \[\frac{\text{Density of the object}}{\text{Density of water}}\] = \[\frac{\rho_{object}}{\rho_{H_{2}O}}\]


What is the Specific Gravity of Water

According to the specific gravity meaning, the specific gravity of water value is equal to 1. However, the temperature of water whose specific gravity is considered is needed to be checked here. At different temperatures, the density of water is different. Therefore, the specific gravity of water value can also change depending on temperature. Additionally, the specific gravity of water can also change due to the presence of impurities in it. Depending on the kind of impurity present in water, water density will vary, and so its specific gravity. The specific gravity of water value for pure water at 4⁰C is 1.


Specific Gravity Value of Other Substances

If you understood what is meant by specific gravity, you would calculate the specific gravity of any substance. There are several applications of specific gravity based on these values. In general, specific gravity for gases is the least, while that of the solids are the most. For example, the specific gravity of dry air is 0.0013. however, the presence of moisture in the air will increase the specific gravity value. Specific gravity for alcohol is 0.82. Following the specific gravity definition, the value for carbon dioxide is 0.00126. Exceptions will be rubber and wood oak, which are solids but have a specific gravity value less than water (0.96 and 0.77, respectively). All these values make up for the different applications of specific gravity, which is discussed in subsequent segments.


How to Calculate Specific Gravity

Till now, it is clear to you what is meant by specific gravity. Using such specific gravity meaning, you will be able to calculate the specific gravity of any substance. For calculation purposes, you need to know the density of the substance at a particular temperature. As stated before, the temperature affects the density of the substances. You can calculate the substance’s density by using a densitometer or divide its mass by its volume. It would help if you also observed what is the specific gravity of water as the base value. For measuring the specific gravity of gases, you must calculate it concerning air. The density of air is 1.20 kg/m³ at room temperature.


Applications of Specific Gravity

There are several applications of specific gravity. Some of them are:

  • The purity of gems can be measured by comparing their value with the ideal sets.

  • Geologists and mineralogists also use these values to determine the mineral content of any rock.

  • Urinalysis experts measure the specific gravity of urine to determine its contents.

  • Students and researchers also learn how to find specific weight from specific gravity. If you want to know how to find specific weight from specific gravity, multiply the specific gravity value with the 1000 (density of water) and 10 (acceleration due to gravity).

FAQ (Frequently Asked Questions)

1. What Do We Learn from the Specific Gravity Chapter in Physics?

The specific gravity chapter in Physics encompasses every aspect related to the question of what is specific gravity. The chapter begins with the specific gravity definition. Then it shows how to use the specific gravity meaning to explain the mathematical concepts. You will not understand what is meant by specific gravity unless you know the density of water. The density of water is also used to understand what is the specific gravity of water. The chapter also discusses the factors that affect the specific gravity of any substance. Although any substance’s specific gravity is defined concerning water, a gas’s specific gravity is calculated for air. Although the specific gravity increases from gases to liquids to solids, that is not always the case. For example, the specific gravity of rubber or wood is lesser than that of water. 

2. How to Find Specific Weight from Specific Gravity for Any Substance at a Given Temperature?

It is possible to calculate the specific weight of any substance from its specific gravity. As per the specific gravity definition, the value is calculated as the density of that substance divided by water density at 4⁰C. To obtain the specific weight of a substance, its specific gravity is multiplied by 1000 (density of water in kg/m³). Finally, the resultant value is multiplied by 10 (acceleration due to gravity value). The final result is the specific weight of that substance. The students and the researchers can use this easy formula for their calculations. Like specific gravity, specific weight is also the characteristic of that substance. Specific weight differs from that of specific gravity since it is the ratio of an object’s weight to its volume. Specific gravity compares the object’s density to the density of water.