Relative density definition: Relative density, also known as specific gravity, is the ratio of a substance’s density to the density of a standard substance. The standard of comparison for solids and liquids is water at 4 °C (39.2 °F), which has a density of 1.0 kg per liter (62.4 pounds per cubic foot). In simple words, the relative density of a substance is the ratio of its density to the density of water at 4 °C (where it is most dense and is taken to have the value 999.974 kg m-3).
If the relative density of a substance is less than one, it is less dense than the reference; if it is greater than one, it is denser than the reference. The densities are equal if the relative density is exactly one; that is, equal volumes of the two substances have the same mass.
Since relative density is a ratio, it lacks units. At 4 degrees Celsius, the relative density of water is one, as this is the standard value used by scientists to determine the relative density of various substances. A water sample was taken at a different temperature or pressure, or one containing impurities has a slightly different density.
Relative density of an object = ρobject / ρwater
ρobect = density of the fluid or object [kg/m3]
ρwater = density of water – normally at temperature 4 °C [kg/m3]
Table of Contents
Daily Life Significance of Relative Density
| Daily Life Examples | Explanation |
|---|---|
| Determining the purity of liquids | Relative density is used to determine the concentration and purity of liquids such as alcohol or honey. |
| Testing the freshness of eggs | The relative density of eggs can be used to test their freshness. Fresh eggs have a higher density than older eggs because the air cell inside the egg grows as it ages, making the egg less dense. |
| Buoyancy | The relative density of an object compared to the density of water determines whether it will float or sink. Objects that are less dense than water will float, while objects that are more dense will sink. |
| Gasoline quality | The relative density of gasoline is an important factor in determining its quality. Higher quality gasoline has a higher relative density, which means it contains more energy per unit volume. |
| Metal identification | The relative density of metals can be used to identify them. For example, gold has a higher relative density than most other metals, which means it can be easily identified by its weight and density. |
| Construction materials | Relative density is used in the construction industry to determine the strength and quality of materials such as concrete or asphalt. |
Relative Density in Simple Terms
Relative density, also known as specific gravity, is a dimensionless quantity that compares the density of a substance to the density of a reference substance, typically water at 4°C (39.2°F).
Mathematically, relative density is expressed as the ratio of the density of the substance to the density of the reference substance:
Relative density = density of substance / density of reference substance
Since both densities are expressed in units of mass per unit volume (e.g. kg/m^3 or g/cm^3), the units of relative density are canceled out, leaving a dimensionless quantity.
For example, if the density of a substance is 1,200 kg/m^3 and the density of water at 4°C is 1,000 kg/m^3, then the relative density of the substance is:
Relative density = 1,200 kg/m^3 / 1,000 kg/m^3 = 1.2
This means that the substance is 1.2 times denser than water at 4°C.
Important Points
| Relative density Definition | Dimensionless quantity that compares the density of a substance to the density of a reference substance, also known as specific gravity. |
| Mathematical Form | Density of substance / Density of reference substance |
| Units | Dimensionless |
| Reference substance | Typically water at 4°C (39.2°F) |
| Example | If density of substance is 1,200 kg/m^3 and density of water at 4°C is 1,000 kg/m^3, relative density of substance is 1.2 |
Summary
- The relative density of an object is defined as the density of that object divided by the density of a reference substance
- It is a relative quantity with no units
- The relative density of water is one at 4 degrees Celsius
More Interesting Topics
Density of Water in g/ml-Accurate Value
The Density of Water lbs/U.S gal
Weight of Water
Unit Weight of Water
The Specific Gravity of Water
Energy Density| Short Overview
Frequently Asked Question
Some of the frequently asked questions are given below
1. How to calculate the relative density of seawater?
The relative density of seawater is the density of a sample of seawater at a specific temperature divided by the density of pure water at a specific temperature.
2. What is the definition of relative density?
Water is a substance that exists in gaseous, liquid, and solid phases and is made up of the chemical elements hydrogen and oxygen. It is one of the most abundant and necessary chemicals. At room temperature, it is a tasteless and odorless liquid with the critical capacity to dissolve many other compounds. Water’s capacity as a solvent is critical to living creatures.
A water molecule consists of two hydrogen atoms attached to the sides of a single oxygen atom.
3. What is the weight of water in kg?
At 25°C (77°F or 298.15K), the weight of water is1 gram per cubic centimeter, or 1 000 kilograms per cubic meter. This means that the density of water is 1 000 kg/m3. Weight per cubic foot: 62.4 pounds per cubic foot [lb/ft3], or 0.58 ounces per cubic inch [oz/inch3]
4. What is the density of water in lbft3?
Density is a physical property that expresses the mass per unit volume. In the case of liquid water, the density of water is close to 1000 kg/m3, though it varies slightly depending on temperature. The density of water lb/ft3 is 62.428 lb/ft3.
More Practice Questions
| # | Exam Questions | Answer |
|---|---|---|
| 1 | What is relative density? | Relative density, also known as specific gravity, is a dimensionless quantity that compares the density of a substance to the density of a reference substance. |
| 2 | How is relative density calculated? | Relative density is calculated by dividing the density of the substance by the density of the reference substance. |
| 3 | What is the reference substance used for determining relative density? | The reference substance used for determining relative density is typically water at 4°C (39.2°F). |
| 4 | What is the unit of measurement for relative density? | Relative density is a dimensionless quantity, so it has no units. |
| 5 | How can relative density be used to determine the purity of liquids? | Relative density can be used to determine the concentration and purity of liquids, such as alcohol or honey, by measuring their relative density compared to water. |
| 6 | What is the relationship between the relative density of an object and whether it will float or sink? | The relative density of an object compared to the density of water determines whether it will float or sink. Objects that are less dense than water will float, while objects that are more dense will sink. |
More Interesting Topics
How Much Does a Gallon of Water Weigh?
How Many Water Bottles is a Gallon| Examples
Energy-The Ability to do Work
Conduction in Physics| Easy Examples
Atmospheric Pressure| Definition & Examples
How Many Cups in a Gallon? Cups to Pints, Quarts, and More
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