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Specific Gravity - Definition, Application, FAQs

Specific Gravity - Definition, Application, FAQs

Vishal kumarUpdated on 02 Jul 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

  1. What is meant by Specific Gravity?/ What is specific gravity?
  2. Specific gravity definition/ specific gravity meaning
  3. SI Unit of Specific Gravity
  4. Application of Specific Gravity
Specific Gravity - Definition, Application, FAQs
Specific Gravity

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.

Commonly Asked Questions

Q: What is specific gravity and how does it differ from density?
A:
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.
Q: How does specific gravity relate to the concept of buoyant force?
A:
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.
Q: Can you explain the concept of API gravity in relation to specific gravity?
A:
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.
Q: Why is specific gravity important in the design of ships and submarines?
A:
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.
Q: How does specific gravity relate to the concept of hydrostatic pressure?
A:
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.

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.

OR

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

Commonly Asked Questions

Q: How does specific gravity relate to the concept of relative density?
A:
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.
Q: Why is water often used as the reference substance for specific gravity?
A:
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.
Q: How does temperature affect specific gravity?
A:
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.
Q: Can specific gravity change with pressure?
A:
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.
Q: What's the significance of specific gravity in brewing and winemaking?
A:
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.

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:

  1. Mixing two or more quantities
  2. 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:

Commonly Asked Questions

Q: Can specific gravity ever be less than 1?
A:
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.
Q: What's the relationship between specific gravity and buoyancy?
A:
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.
Q: How is specific gravity measured in practice?
A:
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.
Q: Why is specific gravity important in the petroleum industry?
A:
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.
Q: How does specific gravity affect the behavior of immiscible liquids?
A:
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.

Frequently Asked Questions (FAQs)

Q: How does specific gravity affect the behavior of fluids in microgravity environments?
A:
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.
Q: Why is specific gravity important in the field of environmental monitoring?
A:
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.
Q: How does specific gravity relate to the concept of fluid compressibility?
A:
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.
Q: Can you explain how specific gravity is used in the field of petroleum engineering?
A:
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.
Q: How does specific gravity affect the behavior of fluids in porous media like soil or rock?
A:
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.
Q: Why is specific gravity important in the design of hydraulic systems?
A:
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.
Q: Can you explain how specific gravity is used in the field of food science and technology?
A:
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.
Q: How does specific gravity affect the behavior of particles in sedimentation processes?
A:
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.
Q: Why is specific gravity important in the field of oceanography?
A:
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.
Q: How does specific gravity relate to the concept of fluid pressure in deep oceans or oil wells?
A:
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.
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