Specific Gravity - Definition, Application, FAQs

Edited By Vishal kumar | Updated on Jul 02, 2025 05:07 PM IST

Introduction
Specific Gravity is the part that comes under Some Mechanical Properties of Matter in the subject of Physics. In this chapter, we will study Specific Gravity, Specific gravity of air, Specific Gravity of water, Specific Gravity of steel, Specific Gravity of Petrol. We will also study about Density and its effect on Specific Gravity and try to understand the term Specific Weight and its Unit. In the last section, we will learn about the density of Iron and Specific Gravity bottles.

This Story also Contains

What is meant by Specific Gravity?/ What is specific gravity?
Specific gravity definition/ specific gravity meaning
SI Unit of Specific Gravity
Application of Specific Gravity

Specific Gravity - Definition, Application, FAQs

NOTE: Sometimes we confuse the term Relative Density and Specific Gravity. We should always remember that both these terms have the same meaning.

Also read -

What is meant by Specific Gravity?/ What is specific gravity?

We will try to understand the concept of Specific Gravity by an example :

One Sunday morning our family member planned a visit to the pool site and for this they were accompanied with rubber tubes. Initially I got confused with the idea of carrying rubber tubes along with them and wondered : How is this thing going to help me swim?. It was like a miracle for me. I didn't sink , I floated . The answer to this miracle was Specific Gravity.

Specific gravity definition/ specific gravity meaning

The term “ Specific Gravity” means weight or density of liquid compared to density of equal volume of water at standard temperature. Sometimes this term is also called Relative Density.

The specific gravity formula is given below.

Specific Gravity= Density of object/Density of Water

Density, it is Physical properties of any substance referring to mass distribution over its total volume. It helps in calculating Specific Gravity.

Density = Mass/Volume

Specific Gravity= Mass of object/Mass of Water

SI Unit of Specific Gravity

As we have seen above in the formula of Specific Gravity , there is the same quantity in the numerator and denominator, so the same unit cancels each other and thus the SI unit of Specific Gravity is not defined or there is no SI unit.

Related Topics Link,

Application of Specific Gravity

Buoyancy

The main application of Specific Gravity is that it decides whether the object will sink or not.

NOTE: If the value of the Specific Gravity comes to be greater than 1 , then the object will sink otherwise it will float.

Distinguish Physical Properties of matter

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Since Specific Gravity is physical properties of matter, it helps in:

Mixing two or more quantities
Distinguish two or more minerals

Specific Gravity of Water

Specific gravity of water is taken as standard value (as it comes to 1) for calculating the Specific gravity of other matter.

NOTE: We calculate Relative Density of matter with respect to density of water calculated at 4◦c and at atmospheric pressure

Specific Gravity of air

In general , Specific Gravity of gas means density of gas with respect to density of water.

Experimentally , Specific Gravity of air equals 0.0013

Formula used: Specific Gravity= Density of object/Density of water

Since, density of air equals 1.3kg per meter cube.

Specific Gravity of Steel

We can calculate Specific Gravity of steel by the help of the above mentioned formula , Since density of different Steel comes to have Different value. Hence it is expected to experience change in Specific Gravity also .

Specific Gravity of Petrol

In case of Fuel, Specific Gravity is given by dividing the density of fuel by density of water

NOTE: We always take units of density in Pounds per Gallon

Also Read:

Specific gravity of soil

The specific gravity of soil is between 2.65-2.85.

Specific gravity of sand

The specific gravity of sand is between 2.65-2.67.

Specific weight

This term generally comes in Fluid Mechanics. In Fluid Mechanics, Specific Weight means Force exerted by the gravity on unit volume of the fluid. In general it is the product of the density of the material and gravitational constant .

Or it can be written as:

?=?g

Its SI unit comes to be Newton per meter cube

Application of Specific weight

It has wide application in soil mechanics as well as in Rock mechanics to determine the maximum stress/load a unit matter can sustain.
It also has a prominent role in Civil Engineering or Mechanical Engineering in determining the tensile strength of mega structures.

Specific Gravity Bottle

Introduction

It is generally constructed from glass for having a clear view of the fluid content inside with a nozzle above to maintain a constant pressure .

Working principle

This apparatus is used to measure Specific Gravity of different fluid by measuring the difference in weight of filled and empty bottle and dividing it with equal volume of water

Formula Used

Sp. Gravity (fluid) = ∆W/Volume of Water

Limitation

A nozzle is fitted on the mouth of the apparatus for the aid of evaporation but it could alter the result because of its weight.

Why is the Specific Gravity test done?

In the medical field: It is done to study the functioning of the kidney, as kidney dilutes Urine. Urine Specific Gravity test compares density of urine to density of water
To study Porosity: Specific Gravity test is done on soil to study porosity of soil or to find void percentage and thus calculate saturation factor.

Also check-

NCERT Physics Notes:

Frequently Asked Questions (FAQs)

1. What is API? How is it related to Specific Gravity?

API Gravity means American Petroleum Institute Gravity. It is a measure of how heavy or light is the fluid (petrol) as compared to the water. It has the base value of 10, if the value is greater than 10 it will float and if this value comes below 10 then it will sink. Hence it works on the same principles of Specific Gravity.

2. Can specific gravity ever be less than 1?

Yes, specific gravity can be less than 1. This occurs when a substance is less dense than the reference substance (usually water). For example, oil has a specific gravity less than 1, which is why it floats on water.

3. What's the relationship between specific gravity and buoyancy?

Specific gravity directly relates to buoyancy. If an object's specific gravity is less than 1 (in water), it will float. If it's greater than 1, it will sink. This is because buoyancy depends on the relative densities of the object and the fluid it's in.

4. How is specific gravity measured in practice?

Specific gravity can be measured using various methods, including hydrometers, pycnometers, or by comparing the weight of equal volumes of the substance and the reference fluid. Modern labs often use digital density meters that calculate specific gravity automatically.

5. Why is specific gravity important in the petroleum industry?

In the petroleum industry, specific gravity is crucial for determining the quality and composition of crude oil and refined products. It helps in classifying oil types, estimating their value, and predicting their behavior during refining and transportation processes.

6. How does specific gravity affect the behavior of immiscible liquids?

When two immiscible liquids with different specific gravities are mixed, they will form layers based on their relative densities. The liquid with lower specific gravity will float on top of the one with higher specific gravity. This principle is used in various applications, from oil spill cleanup to laboratory separations.

7. How does specific gravity relate to the concept of relative density?

Specific gravity and relative density are essentially the same concept. Both refer to the ratio of the density of a substance to the density of a reference substance. The term "specific gravity" is more commonly used in industry, while "relative density" is often preferred in scientific contexts.

8. Why is water often used as the reference substance for specific gravity?

Water is commonly used as the reference substance for specific gravity because it's abundant, easily accessible, and has a density of 1 g/cm³ at 4°C. This makes calculations simpler, as the specific gravity of a substance will be numerically equal to its density in g/cm³ when compared to water.

9. How does temperature affect specific gravity?

Temperature can affect specific gravity because it changes the density of both the substance being measured and the reference substance. As temperature increases, most substances expand and become less dense, potentially lowering their specific gravity. It's important to specify the temperature when reporting specific gravity.

10. Can specific gravity change with pressure?

For most liquids and solids, specific gravity doesn't change significantly with pressure. However, for gases, pressure can have a substantial effect on density and thus on specific gravity. This is why gas specific gravity is usually measured at standard temperature and pressure.

11. What's the significance of specific gravity in brewing and winemaking?

In brewing and winemaking, specific gravity measurements are used to monitor fermentation progress. As sugars are converted to alcohol, the specific gravity of the liquid decreases. Brewers and winemakers use this information to determine when fermentation is complete and to estimate alcohol content.

12. What is specific gravity and how does it differ from density?

Specific gravity is the ratio of the density of a substance to the density of a reference substance, usually water. Unlike density, which is measured in units of mass per volume (e.g., kg/m³), specific gravity is a dimensionless quantity. This makes it easier to compare the relative weights of different substances.

13. How does specific gravity relate to the concept of buoyant force?

Specific gravity is directly related to buoyant force. The buoyant force on an object is equal to the weight of the fluid displaced by the object. If an object's specific gravity is less than that of the fluid, the buoyant force will be greater than the object's weight, causing it to float.

14. Can you explain the concept of API gravity in relation to specific gravity?

API gravity is an inverse measure of the specific gravity of petroleum liquids, developed by the American Petroleum Institute. It's calculated as (141.5 / specific gravity) - 131.5. Higher API gravity numbers indicate lighter oils, which are generally more valuable because they're easier to refine into products like gasoline.

15. Why is specific gravity important in the design of ships and submarines?

Specific gravity is crucial in naval architecture because it determines how a vessel will behave in water. Ships are designed to have an overall specific gravity less than 1 to float, while submarines can adjust their specific gravity to dive or surface by changing their ballast.

16. How does specific gravity relate to the concept of hydrostatic pressure?

Specific gravity directly affects hydrostatic pressure. The pressure at a given depth in a fluid is proportional to the fluid's density, which is related to its specific gravity. Fluids with higher specific gravity will exert greater hydrostatic pressure at the same depth compared to fluids with lower specific gravity.

17. How does specific gravity affect the behavior of gases in industrial processes?

The specific gravity of gases is important in many industrial processes, particularly in gas handling and separation. It affects flow rates, pressure drops in pipelines, and the design of equipment like compressors and gas storage tanks. In gas separation processes, differences in specific gravity can be exploited to separate gas mixtures.

18. How does specific gravity relate to the concept of fluid stratification in storage tanks?

Specific gravity differences can cause fluid stratification in storage tanks, especially for mixtures of immiscible fluids or fluids with varying compositions. This can lead to quality issues, difficulties in mixing or pumping, and potentially dangerous situations if not properly managed. Understanding specific gravity helps in designing tank systems and operating procedures.

19. How does specific gravity affect the flow of fluids in pipelines?

Specific gravity influences fluid flow in pipelines because it affects the pressure and energy required to move the fluid. Fluids with higher specific gravity require more energy to pump and can cause greater pressure drops along the pipeline, which is important in designing and operating fluid transport systems.

20. Why is specific gravity important in the field of hydrogeology?

In hydrogeology, specific gravity is used to understand groundwater flow and contaminant transport. Differences in specific gravity between water and pollutants can cause stratification in aquifers, affecting how contaminants spread and how they can be remediated.

21. How does specific gravity affect the mixing of fluids?

Specific gravity differences can either promote or inhibit fluid mixing. Fluids with similar specific gravities tend to mix more easily, while those with very different specific gravities may form distinct layers. This principle is used in various applications, from cocktail layering to industrial fluid separation processes.

22. What's the relationship between specific gravity and osmotic pressure?

While not directly related, specific gravity and osmotic pressure are both influenced by the concentration of dissolved solutes. Solutions with higher concentrations of solutes generally have higher specific gravities and exert greater osmotic pressures, which is important in biological systems and water treatment processes.

23. How is specific gravity used in the production of batteries?

In battery production, especially for lead-acid batteries, specific gravity measurements of the electrolyte solution are used to determine the battery's state of charge. As the battery discharges, the specific gravity of the electrolyte decreases, providing a way to monitor battery condition.

24. Can you explain how specific gravity relates to the concept of archimedes' principle?

Archimedes' principle states that the upward buoyant force on an object is equal to the weight of the fluid it displaces. Specific gravity determines whether an object will float or sink based on this principle. If an object's specific gravity is less than the fluid's, it will float; if greater, it will sink.

25. How does specific gravity affect the behavior of gases in deep-sea diving?

In deep-sea diving, the specific gravity of breathing gases is crucial. As depth increases, the pressure rises, compressing gases and increasing their effective specific gravity. This can lead to increased breathing resistance and other physiological effects, which divers and equipment designers must account for.

26. Why is specific gravity important in the field of materials science?

In materials science, specific gravity is an important property for characterizing and selecting materials. It helps in understanding material composition, predicting behavior under various conditions, and is often used in quality control processes. It's particularly useful in identifying unknown materials or detecting material defects.

27. How does specific gravity relate to the concept of fluid stratification in lakes and oceans?

Specific gravity differences cause fluid stratification in large bodies of water. In lakes and oceans, variations in temperature, salinity, and dissolved substances create layers of water with different specific gravities. This stratification affects nutrient distribution, aquatic life, and overall ecosystem dynamics.

28. Can you explain how specific gravity is used in the production of concrete?

In concrete production, specific gravity is important for determining the proportions of ingredients. The specific gravity of cement, aggregates, and additives affects the overall density and properties of the concrete mix. It's used to calculate the volume occupied by different components and ensure proper mix design.

29. How does specific gravity affect the behavior of oil spills in marine environments?

The specific gravity of spilled oil relative to seawater determines whether it will float or sink. Most oils have a specific gravity less than 1 and float on water, but some heavy oils may sink. This behavior influences cleanup strategies and the environmental impact of the spill.

30. Why is specific gravity important in the field of gemology?

In gemology, specific gravity is a key property used to identify and authenticate gemstones. Different types of gems have characteristic specific gravities, which can be measured precisely. This helps gemologists distinguish between similar-looking stones and detect synthetic or imitation gems.

31. How does specific gravity relate to the concept of fluid dynamics in blood flow?

While blood flow is primarily governed by other factors like viscosity and vessel diameter, specific gravity plays a role in certain aspects of circulation. For instance, the specific gravity of blood cells relative to plasma affects their distribution in blood vessels and can influence conditions like sedimentation rate in diagnostic tests.

32. Can you explain how specific gravity is used in the production of alcoholic beverages?

In alcohol production, specific gravity measurements are used throughout the process. Initially, it helps determine the sugar content of the starting mixture. As fermentation progresses, decreasing specific gravity indicates the conversion of sugars to alcohol. Final specific gravity measurements can be used to calculate alcohol content.

33. How does specific gravity affect the behavior of particles in centrifugation?

In centrifugation, particles with different specific gravities separate at different rates. Particles with higher specific gravity than the surrounding fluid will sediment faster, while those with lower specific gravity may float. This principle is used in various laboratory and industrial separation processes.

34. Why is specific gravity important in the design of flotation devices?

Specific gravity is crucial in designing flotation devices because it determines buoyancy. The device must have an overall specific gravity less than 1 to float in water. Designers must consider the specific gravity of materials used and the volume of air or other low-density substances needed to achieve the desired buoyancy.

35. How does specific gravity relate to the concept of fluid displacement in volumetric analysis?

In volumetric analysis, specific gravity is important for accurate measurements. When displacing one fluid with another (e.g., in titrations), differences in specific gravity can affect the meniscus shape and the volume reading. Understanding these effects is crucial for precise analytical techniques.

36. Can you explain how specific gravity is used in the field of forensic science?

In forensic science, specific gravity measurements can be used to analyze various types of evidence. For example, it can help identify unknown substances, compare soil samples, or analyze the composition of glass fragments. It's one of many physical properties that forensic scientists use to gather and interpret evidence.

37. How does specific gravity affect the behavior of sediments in rivers and oceans?

The specific gravity of sediment particles relative to water determines their transport and deposition patterns in aquatic environments. Heavier particles (higher specific gravity) tend to settle more quickly, while lighter particles can be carried further by currents. This influences river morphology, delta formation, and ocean floor sediment distribution.

38. Why is specific gravity important in the field of wastewater treatment?

In wastewater treatment, specific gravity is used to design and operate various processes. It affects the settling of solids in sedimentation tanks, the flotation of particles in dissolved air flotation units, and the behavior of sludge in digesters. Understanding specific gravity helps optimize treatment efficiency and equipment design.

39. How does specific gravity relate to the concept of fluid viscosity?

While specific gravity and viscosity are distinct properties, they can be related in some fluids. Generally, liquids with higher specific gravity tend to have higher viscosity, though this is not a universal rule. Both properties are important in understanding fluid behavior in various applications, from lubrication to fluid transport.

40. Can you explain how specific gravity is used in the production of paints and coatings?

In paint and coating production, specific gravity is important for quality control and formulation. It affects the coverage, hiding power, and application properties of the product. Specific gravity measurements help ensure consistency between batches and can indicate whether the correct proportions of ingredients have been used.

41. Why is specific gravity important in the field of environmental monitoring?

In environmental monitoring, specific gravity measurements can indicate the presence of dissolved substances in water bodies. Changes in specific gravity can signal pollution events, saltwater intrusion in coastal aquifers, or stratification in lakes. It's one of many parameters used to assess water quality and environmental health.

42. How does specific gravity relate to the concept of fluid compressibility?

While specific gravity itself doesn't directly measure compressibility, there's a relationship between the two properties. Generally, fluids with higher specific gravity tend to be less compressible. This is particularly relevant for high-pressure applications where fluid compressibility can significantly affect system behavior.

43. Can you explain how specific gravity is used in the field of petroleum engineering?

In petroleum engineering, specific gravity is crucial for characterizing crude oil and natural gas. It affects reservoir fluid behavior, well production rates, and processing requirements. API gravity (derived from specific gravity) is used to classify crude oils and estimate their value. For natural gas, specific gravity influences compression and transportation calculations.

44. How does specific gravity affect the behavior of fluids in porous media like soil or rock?

In porous media, the specific gravity of fluids relative to each other and to the solid matrix affects fluid distribution and movement. This is important in fields like hydrogeology and petroleum reservoir engineering. For example, it influences groundwater flow, oil and gas migration in reservoirs, and contaminant transport in soil.

45. Why is specific gravity important in the design of hydraulic systems?

In hydraulic systems, specific gravity affects the pressure generated by a column of fluid, the force exerted by hydraulic cylinders, and the power required to pump the fluid. Designers must consider the specific gravity of hydraulic fluids when calculating system pressures, sizing components, and estimating power requirements.

46. Can you explain how specific gravity is used in the field of food science and technology?

In food science, specific gravity measurements are used for quality control, process monitoring, and product development. It can indicate sugar content in beverages, fat content in milk, or air incorporation in whipped products. Specific gravity also affects the behavior of foods during processing and storage.

47. How does specific gravity affect the behavior of particles in sedimentation processes?

In sedimentation processes, particles with higher specific gravity than the surrounding fluid will settle faster. The rate of sedimentation is proportional to the difference in specific gravity between the particles and the fluid. This principle is used in various separation and purification processes in industries and wastewater treatment.

48. Why is specific gravity important in the field of oceanography?

In oceanography, specific gravity (often expressed as density) is crucial for understanding ocean circulation, mixing processes, and the distribution of marine life. Variations in specific gravity due to temperature and salinity drive major ocean currents and influence the vertical structure of the ocean, affecting nutrient distribution and marine ecosystems.

49. How does specific gravity relate to the concept of fluid pressure in deep oceans or oil wells?

Specific gravity directly affects fluid pressure at depth. In deep oceans or oil wells, the pressure at a given depth is proportional to the specific gravity of the overlying fluid column. This is crucial for designing deep-sea equipment, planning drilling operations, and understanding the behavior of fluids in high-pressure environments.

50. Can you explain how specific gravity is used in the production of pharmaceuticals?

In pharmaceutical production, specific gravity is used for quality control, formulation, and process monitoring. It can indicate the concentration of active ingredients in solutions, help in the design of drug delivery systems, and ensure consistency in liquid medications. It's also used in the production of suspensions and emulsions to ensure stability and proper mixing.

51. How does specific gravity affect the behavior of fluids in microgravity environments?

In microgravity environments, such as in space, the effects of specific gravity differences are greatly reduced. Fluids that would normally separate due to specific gravity differences on Earth may remain mixed in space. This has implications for fluid handling in spacecraft systems and for scientific experiments conducted in microgravity conditions.