Specific Gravity

Introduction to Specific Gravity

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. In this chapter about Specific Gravity, we will be going to deal with Explanation, Formula, Calculation, and its applications. 


Definition: What is Specific Gravity?

Physics is more of a practical subject. And, if you want to understand it properly and in-depth, you must be thorough with the concept of specific gravity.

Specific gravity is also known as relative gravity. It does not have any dimension which implies that it is a dimensionless quantity. It can be defined as the ratio of a substance’s density to that of water at a particular given temperature. It is important to note that temperature plays a vital role in determining the specific gravity of any substance. Therefore, specific gravity is a property of the substance at a particular temperature. Besides, pressure also affects the specific gravity of any substance.

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

\[SG = \frac{\rho_{substance} }{\rho _{water}}\]

In general, the specific gravity of any substance is defined relative to 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.

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


What is the Specific Gravity of Water?

According to the meaning of specific gravity, the specific gravity of water value is equal to 1. However, the temperature of water whose specific gravity is considered needs to be considered 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.

In ideal conditions, the specific gravity of water value for pure water at 4⁰C is 1.


Specific Gravity of Other Substances

If you now understand the meaning and concept of specific gravity, you will be able to 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 the subsequent segments.


How to Calculate Specific Gravity?

Till now, it has been clarified to you what the meaning of specific gravity is. With the application of the concept that you’ve understood, you will be able to calculate the specific gravity of any substance.

For calculation purposes, you will 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 the specific gravity of water is 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. 

  • Gemologists use it to distinguish similar gems.

  • 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.

  • Checking on the progress of reactions and the concentration of solutions.

  • Testing  battery fluid and antifreeze.

  • 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).


Points to ponder about Specific Gravity

  • Specific gravity is a dimensionless quantity. That means it can be represented as fundamental units raised to power zero. M0 L0 T0. This also means that specific gravity does not have any units.

  • One of the reasons why specific gravity is a unitless quantity is that it is the ratio of two quantities with same dimensions or units.

  • Specific gravity is simply the ratio of two densities of two objects or substances.

  • In most of the cases of specific gravity, it is defined as the ratio of density of the substance with respect to density of water. 

  • Specific gravity of water is unit i.e Specific Gravity (water) = 1

  • If the specific gravity of a substance is greater than 1, it will sink into the water. Objects such as rocks, metals, etc which are very dense in nature are most likely to float as they have specific gravity more than 1.

  • If the specific gravity of the substance is less than 1, the substance will float on the surface of the water instead of sinking into it. As such objects will have density values less than that of water, the ratio will be less than one. Paper, hair, dust, oil, etc are such examples where the specific gravity value is less than 1.

  • Specific gravity values are affected by the temperature and pressure of the environment or the surroundings.

  • Generally, specific gravity is measured at 40 C. The specific gravity of water is equal to 1 at 40 C. It is very important to note that this value will change as there will be a change in temperature.

  • As temperature increases, a substance can undergo melting (solid to liquid) or evaporation (liquid to gas), or sublimation (solid to gas directly). This will result in a change in the density of the substance as solids are said to be the most dense among three and gases hold less density while the density of liquid lies between these two values. Hence, specific gravity changes with a change in temperature.

  • To compare two specific gravities, make sure both of them are at the same temperature and pressure configuration. 

  • The pressure surrounding the system of the substance affects specific gravity as pressure and volume are inversely proportional. Also, volume is inversely proportional to the density of the substance. Hence, we can conclude that specific gravity is directly proportional to the pressure experienced by the substance in the given system.

  • The specific gravity of water at 1 atm pressure and 40 C = 1

The specific gravity of water at 1 atm pressure and 250 C = 0.9970

FAQs (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 specific gravity is. 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.

3. What are a few applications of specific gravity?

Specific gravity has a lot of applications in physics. It is directly related to buoyancy. When the specific gravity of a certain substance is less than the specific gravity of the fluid it is immersed in, the substance will float over the fluid. In the case of liquids, specific gravity is an important parameter to determine the viscosity of the liquid. Specific gravity concepts are widely used in the oil industry. Hence specific gravity finds itself used in many sectors especially ones related to liquids.

4. What are the factors that affect specific gravity?

Specific gravity is a physical parameter of the liquid. It is affected by the temperature and pressure of the environment. We can simply say that for specific gravity of a substance, say water, can vary if the temperature of the surrounding has changed or the system which is storing the liquid is exposed to external pressure. Hence, while dealing with specific gravity, it is very important to note down the temperature and pressure of the environment and while comparing two specific gravities, it should be made sure that both of them are observed in the same temperature and pressure.

5. How can Vedantu help me understand the concepts from physics?

Vedantu is a leader in online tutoring and has established itself as a reliable source of information among students. The concepts on Vedantu are explained in a simple and easy-to-understand manner along with books and important concepts that students should go through before appearing for the exams. Vedantu provides quality and up-to-date educational information to students and students should take advantage of these resources. Just like the concept of Specific Gravity, students can find more concepts related to physics on Vedantu.

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