Density and specific gravity are two concepts that are often used in physics and other sciences to describe the properties of materials or substances. Although both are related to the weight and volume of an object, they have different meanings and are measured in different units. Here is a brief introduction to the difference between density and specific gravity:

Density:
 Density is a quantity that measures how much mass (the amount of matter) contained in a certain volume.
 Density is expressed in units of mass per volume, such as kilograms per cubic meter (kg/m³) in the international system (SI).
 Example : If you have 1 kilogram (kg) of sugar and you put it in a container with a volume of 1 liter (1,000 cm³), then the density of the sugar is 1 kg/m³.

Specific Gravity:
 Specific gravity is a quantity that measures how much gravitational force acts on an object due to the mass of that object in comparison with the gravitational force acting on the same volume of pure water at a certain temperature.
 Specific gravity is expressed in units that have no dimensions, such as Newtons per cubic meter (N/m³) or pascals (Pa) in the SI.
 Usually, pure water at a temperature of 4 degrees Celsius is used as a standard for measuring specific gravity, and the specific gravity of water at that temperature is around 1,000 N/m³ or 1,000 kg/m³.
The main difference between the two is that density is an intrinsic property of a substance that does not depend on the force of gravity, whereas specific gravity is a measurement of a property of a substance that depends on the force of gravity. The density of a substance will remain constant anywhere in the universe, whereas the specific gravity of a substance will change if you measure it on a different planet with a different gravitational acceleration.
To summarize, density measures how dense the matter is in a volume, while specific gravity measures how heavy an object is in comparison to the weight of water at a certain temperature and pressure.
To understand more about the difference between density and specific gravity. So you can read a more detailed explanation regarding the Differences in Density and Specific Gravity below.
What is Density and What is Specific Gravity?
Let’s discuss the basic definitions of density and specific gravity:

Density:
 Density is a physical quantity which measures how much mass (amount of matter) is contained in a certain volume.
 Mathematically, density (?) is defined as the mass (m) of an object divided by the volume (V) of that object:
$rho = frac{m} {V}$  Density is measured in mass units per volume, such as kilograms per cubic meter (kg/m³) in the international system (SI).

Specific Gravity:
 Specific gravity is a physical quantity that measures how much gravitational force acts on an object due to the mass of that object in comparison with the gravitational force acting on the same volume of pure water at a certain temperature.
 Mathematically, weight type (?) is defined as the weight (W) of an object divided by the volume (V) of that object:
$?=VW?$  Specific gravity is measured in dimensionless units, such as Newtons per cubic meter (N/m³) or pascal (Pa) in SI.
 Pure water at a temperature of 4 degrees Celsius is often used as a standard for measuring specific gravity, and the specific gravity of water at that temperature is about 1,000 N/ m³ or 1,000 kg/m³.
So, in short, density is a measure of how dense an object or substance is in a certain volume, while specific gravity is a measure of how dense an object or substance is in a certain volume. how heavy an object is in comparison with the weight of water at a certain temperature and pressure.
Units of Measurement
Both quantities, namely density and specific gravity, have different units of measurement:

Density:
 The unit commonly used to measure density is the kilogram per cubic meter (kg/m³) in the international system (SI).
 Example: If the mass of an object is 2 kilograms (kg), and the volume of the object is 0.5 cubic meters (m³), then the density is $frac{2 , text{kg}}{0.5 , text{m³}} = 4 , text{kg/m³}$.

Specific Gravity:
 The units commonly used to measure specific gravity are Newtons per cubic meter (N/m³) or pascals (Pa) in SI.
 Usually, specific gravity is measured by comparing the weight of an object with the weight of the same volume of pure water at a certain temperature and pressure, so the unit of measurement is dimensionless.
 For example, the specific gravity of water at temperature 4 degrees Celsius is about 1,000 N/m³ or 1,000 Pa.
These two units reflect the fundamental difference between density (which relates to mass per volume) and specific gravity (which relates to weight per volume). Density is measured in units that describe mass per volume, while specific gravity is measured in units that describe force per volume.
Focus on the Amount of Matter in an Object
The concept of mass is one of the concepts basic physics that focuses on the amount of matter or ingredients contained in an object. Mass is a physical quantity that measures the amount of matter or particles present in an object. Basically, mass is a measure of how heavy or how much matter is contained in an object.
Some important points about the concept of mass are:

Properties Intrinsic: Mass is an intrinsic or inherent property of an object. This means that the mass of an object remains the same wherever the object is in the universe, and does not depend on certain conditions or locations.

Mass Unit: Unit The general term for mass in the international system (SI) is kilogram (kg). However, depending on the context, other units such as grams (g) or tons (1,000 kg) are also often used.

Mass Measurement: The mass of an object can be measured using special tools such as scales. Scales work by measuring the force that arises due to the mass of an object placed on it.

Conservation of Mass: The principle of conservation of mass states that in a closed system, mass The total system remains constant, as long as no material enters or leaves the system. This principle is one of the basics in chemistry and physics.

Relationship with Weight: Mass and weight are two related but different concepts. Mass is a measure of the amount of matter in an object (expressed in kg), while weight is the gravitational force acting on the object (expressed in newtons, N). The relationship between mass and weight is weight = mass × gravitational acceleration (W = m × g), where the gravitational acceleration (g) is 9.8 m/s² on the earth’s surface.
By understanding the concept of mass, we can measure and understand the basic properties of matter and explain many physical and chemical phenomena related to the amount of matter involved. Mass is also the basis for calculating other quantities such as density, specific gravity, and many other physical concepts.
Concept of Weight
The concept of weight is closely related to the influence of gravitational force on the mass of an object. Weight is a physical quantity that measures the gravitational force acting on an object due to the object’s mass. Some important points about the concept of weight are:

Gravitational Force: Weight is the result of the gravitational force exerted by a planet or other large object on an object that has mass . This gravitational force pulls the object towards the center of mass of the large object.

Weight Units: The common unit for weight in the international system (SI) is the newton ( N). The newton is a unit for force, and 1 newton is equivalent to the gravitational force exerted on an object with a mass of 1 kilogram (kg) by a gravitational acceleration of approximately 9.8 meters per second squared (m/s²) on the surface of the earth.

Relationship with Mass: Weight (W) and mass (m) are related through the following formula:
$W = m cdot g$
where: W is the weight in newtons (N).
 m is the mass in kilograms (kg) .
 g is the local gravitational acceleration at a certain location (for example, 9.8 m/s² on the earth’s surface).
This means that the weight of an object is the product of its masses the object with gravitational acceleration at that location. This explains why the weight of an object can be different on different planets or celestial bodies because the gravitational acceleration is different in each place.

Difference between Mass and Weight: Mass is an intrinsic property of an object that measures the amount of matter in the object. Mass remains constant wherever the object is located in the universe. Meanwhile, weight is a measurement of the gravitational force that acts on the mass of an object. Weight can vary depending on the gravitational acceleration at that location.
By understanding the concept of weight, we can explain why we feel heavier on the surface of the earth than on other planets that have gravitational acceleration lower, and why objects fall towards the center of the earth due to the influence of gravitational force. Weight is an important quantity in physics and engineering because understanding how gravitational forces affect objects is highly relevant in a variety of contexts, including mechanics, dynamics, and astronautics.
Comparison of Values
Density ( ?) and specific gravity (?) are two quantities that are often used in physics and materials science. Although both are related to the material properties of an object, they have different values and units. Here, we will compare the values and relationships between density and specific gravity:

Density (?):
 Density is a quantity that measures how dense or heavy a substance is in a certain volume.
 The international unit commonly used for density is the kilogram per cubic meter (kg/m³).
 Example: The density of water is around 1,000 kg/m³.

Specific Gravity (?):
 Specific gravity is a quantity that measures how much gravitational force acts on an object due to the object’s mass in comparison with the gravitational force acting on the same volume of pure water at a certain temperature and pressure.
 The units used for specific gravity are Newtons per cubic meter (N/m³) or pascals (Pa), but specific gravity is also often expressed without units (dimensions).
 The specific gravity of water at a temperature of 4 degrees Celsius is around 1,000 N/m³ or 1,000 Pa.
The relationship between density and specific gravity is as follows:
$gamma = rho cdot g$
where:
 ? is the specific gravity (in N/m³ or Pa).
 ? is the density (in kg/m³).
 g is the local gravitational acceleration ( in m/s²).
So, to calculate the specific gravity of a substance, you can multiply its density by the value of the local gravitational acceleration at a certain location. Because the acceleration of gravity is usually close to 9.8 m/s² at the surface of the earth, the specific gravity of water is about 1,000 N/m³ or 1,000 Pa when measured on the earth.
Thus, density and specific gravity are closely related, but differ in their units and focus of measurement. Density measures how dense a material is in a certain volume, while specific gravity measures the gravitational force acting on that material in comparison to water at a certain temperature and pressure.
Practical Measurements
Measuring mass type and specific gravity of a material can be done in various ways depending on the resources and equipment you have. Here, I will explain how to measure density and specific gravity practically:
How to Measure Density:

With Scales and Volume Measurements:
 Take a sample of the material whose density will be measured.
 Weigh the sample using an accurate balance to obtain the mass (m).
 Measure the volume of the sample with an appropriate volume measuring instrument, such as a measuring cylinder or other measuring instrument, to obtain the volume (V).
 Calculate the density (?) with the formula ? = m/V.

By Floatation:
 This is a classical method for measuring the density of objects that are denser than liquid.
 Hang the object on a spring balance in air and record its weight (W1).
 Next, immerse the object in a liquid (for example water) and record its weight when it sinks (W2 ).
 The density of the object can be calculated using the formula ? = (W1 W2)/[(W1 W2) Wair].
How to Measure Specific Gravity:

Using Scales and Volume Measurements:
 Weigh an object to get the weight (W) of the object.
 Measure the volume of the object with a suitable volume measuring instrument, such as a graduated cylinder.
 Calculate the specific gravity (?) with the formula ? = W/V.

Using a Pycnometer:
 A pycnometer is a special instrument designed to measure the specific gravity of liquids or solid.
 Fill the pycnometer with the liquid whose specific gravity you want to measure.
 Weigh the pycnometer containing the liquid to get the total weight (W1).
 Next, empty the pycnometer and weigh the empty pycnometer (W2).
 The specific gravity of the liquid can be calculated by the formula ? = (W1 W2)/(W2 Wair).
Make sure you understand the basic principles of measuring density and specific gravity and follow appropriate safety guidelines when using equipment and chemicals. In addition, make sure to calibrate your measuring tools to get accurate results.
Uses in Science
Density and specific gravity have an important role in various fields of science, especially in physics, materials science, and engineering science. The following are some examples of the use of both in various fields:
1. Physics:
 Mechanics: In mechanics, the concept of specific gravity is used to understand the behavior of bodies in a gravitational field. Density and specific gravity are used in solving problems related to pressure, buoyancy, and the motion of objects in fluids (hydrodynamics).
 Thermodynamics: In thermodynamics, density is used to calculate the density of materials in various temperature and pressure conditions. This is important in understanding phase changes in materials, such as evaporation and solidification.
2. Materials Science:
 Metallurgy: Density and specific gravity are used to measure the physical characteristics of metals and metal alloys, which are important in the manufacturing and processing of metals.
 Geology: In geology, information about the specific gravity of rocks and minerals is used to identify rock types and evaluate their properties, such as strength, composition, and structure.
3. Civil and Building Engineering:
 Building Structure: Density is used for the design and analysis of building structures, especially in determining the structural load and bearing capacity of the soil beneath building.
 Dam Construction: The density of soil and rock is a key factor in planning and building a dam, which must be able to withstand the pressure of water and the mass of soil above it.
4. Geophysical Sciences:
 Earth Research: Density and specific gravity are used in geophysical research to understand the composition of the earth, including the study of the earth’s layers, the earth’s crust, and the earth’s mantle.
5. Ocean and Ocean Sciences:
 Oceanography: The density of sea water is very important in understanding ocean circulation and the formation of thermocline layers in the ocean.
6. Chemistry:
 Physical Chemistry: In physical chemistry, the specific gravity of chemical substances is used in relation to thermodynamic properties and molecular interactions.
7. Medicine and Health:
 Medicine: The specific gravity of fluids in the human body can have implications in medical diagnosis and health assessment.
The use of density and specific gravity is very diverse and important in understanding the properties of materials, designing structures, and scientific research in various fields. They provide important insight into how matter interacts with its environment and have broad practical applications in engineering, the environment, and the natural sciences.
Impact of Temperature
Temperature has a significant impact on density and specific gravity of the substance. Temperature variations can change the physical properties of a material, which in turn affects density and specific gravity. Following are some concepts that explain changes in density and specific gravity with temperature:
Variation of Density with Temperature:

Thermal Expansion : Most materials will experience thermal expansion when heated. This means they will enlarge and become less dense. Since density is mass per volume, if the volume of a material increases due to thermal expansion, then the density will decrease. This means that the density tends to decrease with increasing temperature.

Relation to Water: Water is a good example to explain the change in density with temperature. The density of water at a temperature of 4 degrees Celsius is around 1,000 kg/m³. However, when water is heated, its density decreases. At temperatures above 4°C, the density of water will be lower than 1,000 kg/m³, and at temperatures below 4°C, the density will be higher.
Variation of Specific Gravity with Temperature:

Specific Gravity Measurement: Specific gravity is the ratio of the weight of an object to the weight of the same volume of water at a certain temperature and pressure. Because the volume weight of water at a temperature of 4 degrees Celsius is used as a standard, changes in temperature will affect specific gravity.

Changes in Fluid Specific Gravity: Temperature affects weight type of fluid, especially fluids that experience significant thermal expansion, such as gas. When a gas is heated, its specific gravity tends to decrease, and conversely, when a gas is cooled, its specific gravity tends to increase.

Examples in Marine Science: In the ocean, changes in temperature with depth can affect the specific gravity of seawater. When sea water temperature decreases with depth (thermocline), the specific gravity of sea water will also vary, which can affect the movement and acoustic properties of sound waves in the sea.
In many scientific contexts and technical, it is important to consider temperature variations when measuring or using data about density and specific gravity. Changes in temperature can have a significant impact on the properties of fluids and materials, and they must be taken into account in planning and analysis in fields such as ocean science, geology, and civil engineering.
Relation to Volume
Density and specific gravity have a close relationship with the volume of an object. This relationship relates to how the volume of an object affects the calculation of density and specific gravity. Below, I will explain the relationship between the two in terms of object volume:
Relationship of Density to Object Volume:

Density Formula
strong>: Density (?) is defined as the mass (m) of an object divided by the volume (V) of that object, as in the following formula:
$rho = frac{m}{V}$ 
Effect of Volume: Density is a measure of how much mass is contained in a certain volume. In other words, as the volume of an object increases, its density tends to decrease if the mass of the object remains constant, and vice versa. This means that if you change the shape or size of an object that has a fixed mass, its density will change according to the change in volume.

Example: For example, if you have a block of constant mass, then you cut it into two pieces with a smaller volume, the density of each piece will be greater than the density of the original block, because the fixed mass is divided by a smaller volume.
Relationship of Specific Gravity with the Volume of an Object:

Specific Gravity Formula: Specific gravity (?) is defined as the weight (W) of an object divided by the volume (V) of that object, as in the following formula:
$gamma = frac{W}{V}$