In this article, we will learn what is specific gravity, it’s definition, meaning, formula, equation, examples, calculation, how to derive it from density, etc. are elaborated in this article.

Let’s explore!

## What is Specific Gravity? Definition, Meaning

### What Does Specific Gravity Mean?

When setting up the mixer, it is important to understand the specific gravity of the fluid to be mixed because it affects the torque and horsepower required to mix the fluid properly.

When we go out in the summer to enjoy the pool and the river, we always have to make sure that all our equipment and safety measures are working and in place. When we go to the river to board the boat, we have to make sure the boat is not leaking and wear safety vests.

For young children who are still learning to swim, we make sure they bring floats or we swim with them in a swim ring to make sure they don’t sink. Why do the boat and the swimming ring float? There are many factors that determine whether an object will sink or float in water, one of which is what we call specific gravity.

- In higher specific gravity applications, more torque is required to produce the desired results.
- If the specific gravity is not considered and the mixer is not optimized accordingly, the result will be unpredictable and engine damage and/or failure may occur.

In this blog, we are going to study about the specific gravity and its different aspects. Proportion is a concept that we have all seen but don’t know its name. In addition, we will discuss specific gravity, specific gravity formulas, and their derivation, as well as calculation examples on this topic.

You can learn: What is Cavitation

### Specific Gravity Definition

Specific gravity refers to the relationship between the density of an object and the reference substance. In addition, the specific gravity can tell us whether the object will sink or float in the reference material.

In simple terms, specific gravity defines whether an object sinks or floats in the water. In addition, there are many factors that determine whether an object floats or sinks.

**Specific gravity is the ratio of the density of the object to the reference substance**. Specific gravity can tell us whether an object will sink or float in our reference material based on its value. Normally reference substance is used as water.

## Specific Gravity Examples

When you throw a penny to the water source to wish, the feather carries the bottom. It’s because the penny is dense with water. If it is connected to a specific gravity formula for our purpose, we believe that specific gravity is greater than 1. If the specific gravity is greater than 1, the object sinks, and when the specific gravity is less than 1, the object will float. If the specific gravity is equal to 1, this does not allow the object to rush into the liquid.

When considering the density of unknown materials, specific gravity is an important measurement index.

The relationship between unknown materials and more common materials allows quick comparisons in terms of density. For gases, air at normal pressure and temperature is often used as reference material.

For liquids, water is often used as the reference material. An example of comparing two liquids is when kerosene has a value of less than 1 compared to pure water at 40 ° F (104 ° C) at normal atmospheric pressure. This means that the density of kerosene at this temperature is less than that of water.

This also means that when both are placed in a container, the kerosene will float on the water. What is needed to calculate specific gravity is the material and its density, the reference material, and its density, temperature, and pressure? Then, the material being evaluated will measure its density at a given temperature and pressure and will assign it a number less than, equal to, or greater than 1, depending on their differences. Relative to the density of the reference material-related questions.

- Specific gravity is the basis for the historical methods used to concentrate ore. Panning, jigging, shaking, spiral separation, and heavy media separation are one of the methods for obtaining concentrates based on differences in specific gravity.
- Specific gravity is the highest among rocks rich in iron, magnesia, and heavy metals, and the lowest among rocks rich in alkali, silica, and water. Because specific gravity can be calculated quickly and precisely, it is widely used in chemical science and technology; for example, determining specific gravity is a common element of the characterization of new liquid compounds.
- The specific gravity of most organic molecules having solely carbon, hydrogen, and oxygen is less than one. The apparatus that is used to measure specific gravitational forces.

So, what exactly is density? The density of an object in a particular volume is a measure of how compact or heavy it is. We measure density in grams per milliliter (g/mL), grams per cubic centimeter (g/cm3), or kilograms per liter (kg/L), which are all units of mass per unit volume.

## Factors Affecting the Specific Gravity

- As discussed, specific gravity is a measure of the density of an object compared to the density of water at precise temperature and pressure.
- The density of objects and liquids sort of depending upon the change in pressure and temperature and that’s the reason why it does affect the specific gravity.
- Use standard temperature and pressure when calculating specific gravity. If the external influence is not adjusted, the proportion will change.
- Now let’s look into specific gravity of milk. The density of milk is affected by the combined density of its various components. Therefore, it depends on the amount of dissolved or suspended matter, the change in composition, and the physical state of the milk ingredients.
- The density of milk is also affected by several factors, such as the temperature history of the sample, biological differences in micelles, and milk processing conditions. Among various milk ingredients, the fat content of milk is known to be the main reason for the change in milk density. The physical state of milk fat has been observed to have a greater impact on density.

## Formula & Equation of Specific Gravity

By assuming the water as a reference substance, the formula for specific gravity is a division of the density of any object which is then divided by the density of water.

- Specific Gravity = density of any object/density of water.
- (SG) = ρ
_{object}/ ρ_{water}

Where S.G = Specific Gravity

## Unit of Specific Gravity

We get from the formula of specific gravity,

- Specific Gravity = density of any object/density of water.

To find out the unit,

- Unit Specific Gravity = Unit of the density of any object/Unit of the density of water
- Unit Specific Gravity = Unit of the density/Unit of the density
- Unit Specific Gravity = Unitless

Specific gravity has no unit, because the numerator and denominator have the same unit, so they just cancel each other out.

Let’s look at an example. The density of a substance is 20 gm/mL [density in C.G.S] and the density of water is 1 gm /mL [density in C.G.S]

From the equation,

- Unit Specific Gravity of substance = density of substance /density of water
- Unit Specific Gravity of substance = [20 gm/mL] /[1 gm /mL]

We cancel the unit g/mL in both the numerator and the denominator as both are the same. So, it is unitless.

The picturization of high and low density is as follows:

Density is directly related to the mass of the object (unit: usually in grams, but can also be in kilograms or pounds), so the specific gravity can also be determined by dividing the mass of the object by the mass of water.

Note that all these units are the same, so the result will not have units because they cancel each other out.

Now let’s look at the specific gravity of different materials under normal physical conditions:

Let’s understand this subject better by looking into solved examples:

## How to Get Specific Gravity from Density?

It is simple, only need to use the specific gravity formula,

The formula or equation of specific gravity is written as follows:

⇒ SG_{substance} = ρ_{substance} / ρ_{H2O}

⇒ Specific gravity of any substance = Density of that substance/density of water

⇒ Specific gravity of any substance = Density of that substance in kg/m^{3} /1000 in kg/m^{3}

Now, if the data of density of any substance is given, then we can find out the specific gravity of using above formula.

## How to Get Density from Specific Gravity?

It is very easy to get density from specific gravity, let’s see how to get it?

The formula or equation of specific gravity is written as follows:

⇒ SG_{substance} = ρ_{substance} / ρ_{H2O}

⇒ ρ_{substance} / ρ_{H2O} = SG_{substance}

⇒ ρ_{substance} = SG x ρ_{H2O}

⇒ Density of any substance = Specific gravity of that substance x density of water

⇒ Density of any substance in kg/m^{3} = Specific gravity of that substance x 1000 kg/m^{3}

Now, if the data of specific gravity of any substance is given, then we can find out the density using above formula.

## Specific Gravity Calculation Examples

### Example 1: Calculation of specific gravity of Iron

Calculate the specific gravity of iron. The density of iron is 7850 kg / m3. The specific gravity of iron and water is calculated as follows:

(SG)iron = [7850 kg/m^{3}] / [1000 kg /m^{3}] = 7.85

Therefore, the specific weight of iron calculated as 7.85

### Example 2: Calculation of Specific gravity of Gold

If the density of gold is 19300 kg/m^{3}, what is the specific gravity of gold?

We can calculate the specific gravity of gold as follows:

(SG)gold = [19300 kg/m^{3}] / [1000kg/m^{3}] = 19.3

Therefore, the specific gravity of iron is 19.3.

### Example: Calculation of density of the ice

If the specific gravity of the ice is 0.92, what is the density of the ice? The density of ice can be calculated using the exchange specific gravity formula as follows:

(SG) = ρ_{substance} / ρ_{H2O}

⇒ρ_{substance} = SG⋅ρ_{H2O}

Substituting the above formula, we obtain

Ρ_{substance} = 0.92 x1000 kg/m^{3} = 920 kg/m^{3}

## Methods for Determining Specific Gravity

The oil and gas industry uses many different types of instruments to determine specific gravity.

### Effusion and Weighing Technology

The most famous exudate and the weighing instrument is a gravity balance. The principle of operation of a gravity balance is to measure the pressure exerted by a gas of a given density and the pressure exerted by air of the same density, and the specific gravity is determined by the ratio of these pressure measurements.

In this instrument, the device used to measure the buoyancy exerted on objects suspended in gas or air is provided by a balance beam, one end of the balance beam has a sealed float and the other end has a balance weight and a scale A. When the buoyancy of the continuously tested gas sample and the air are equal, the density is equal.

### Direct Weighing Technology

The UGC gravimeter is the most widely used direct weighing instrument. The same tank, called the reference and sample, is suspended at each end of the balance beam, equidistant from the pivot axis.

Pressure, temperature, and other environmental changes have the same effect on the two storage tanks, thus compensating for these changes. For example, by using a particularly suitable pressure regulator, the reference tank air pressure can be used to adjust the air pressure of the sample tank to eliminate the influence of ambient temperature fluctuations. The ambient temperature that controls the pressure in the sealed reference tank can control the pressure in the sample tank. Only the real change in specific gravity is recorded, and the obvious change due to changes in ambient temperature will not be recorded. Calibration is performed by using a calibration disc equal to the weight difference between “full scale” gravity and “low scale” severity.

## Applications of Specific Gravity

There are many applications for specific gravity. Some of them are:

- By comparing the values of gems with an ideal set, one can calculate the purity of gems.
- Values of specific gravity of any substance can be used by geologists and mineralogists to determine the mineral content of any of the rocks.
- A urinalysis specialist measures the specific gravity of urine to determine its content.
- Students and researchers also learn to find proportions from among them.
- In pharmacy, it is sometimes necessary to use the concepts of density, specific gravity and specific volume to determine the weight and volume of certain liquids.

## High Rated Course

Intro to Fluid Mechanics for Engineering Students Part 1

Intro to Fluid Mechanics for Engineering Students Part 2

## Conclusion

In above blog we have learned a lot about specific gravity since it is crucial part of science and measurement areas. Also there will be a time when we will require exact weight of liquids and volumes of solids mainly while compounding and that’s why the determination of specific gravity is very much important. For the better understanding of the concept we even studied some of the examples.

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