Unit of Density: Definition, SI Unit & Symbol

The density of a material is defined as the denseness of that particular material in a specific given area.

• The density of the material refers to its mass per unit volume.
• It is generally a measurement of how tightly the matter particles are packed together.
• Various materials have different densities based on the intermolecular forces involved in packing.
• The density of water, i.e. 1 gram/cubic centimeter, is commonly used as the standard value for calculating the density of different substances.

Density is measured with the SI unit as Kilograms per cubic meter (kg/m³). Density definition – Density is defined as the relationship between the substance’s mass and the volume it occupies.

In qualitative terms, it indicates how heavy an object can be at constant volume. The density of different substances is different which means that the different substances with similar volumes will weigh differently.

Unit of Density for Liquids and Solids

Also Read: Properties of Fluids

If we talk about other density units, metric tons and liter are also used despite the fact that they are not part of the SI unit system. The other units of density are as follows:

• Gram per millilitre (g/mL)
• Gram per cubic centimeter (g/cm³) -------- 1 g/cm³ = 1000 kg/m³
• Kilogram per cubic decimetre (kg/dm³)
• Metric ton per cubic meter (t/m³)
• Kilogram per litre (kg/L)
• Megagram (metric ton) per cubic meter (mg/m³)

Even though the SI unit of density is kg/m³, the other commonly used units to measure density are:

• Solids - g/cm³
• Liquid - g/ml
• Gases - g/L 

Furthermore, the CGS unit of density is gram per cubic centimeter (g/cm³). 

The density of an object can be calculated by the formula:

ρ = m/v

Where Density symbol represents,

• ρ = Density of the object
• m = Mass of the object
• v = Volume of the object

The particles in solids are tightly packed with very little space between them, therefore the solids are denser than liquids and gases. The liquids are less dense than solids because the particles are not tightly packed in liquid but denser than gases which contain free-flowing particles.

Density Formula

To understand the concept of density better, let us look at a couple of examples:

• Lead, iron, and platinum are various examples of dense materials. Materials with high density are harder and they are more “likely” to feel heavy. 
• Aluminium, glass, and bamboo are some examples of sparse materials which are the opposite of dense materials.

Let us look at the densities of some substances:

Generally, we can observe that solids are denser than liquids and liquids are denser than gases. The reason behind this is that the particles in solids are densely packed. For liquids, the particles are somewhat loose and can slide across each other while for gases the particles are loose and free to move around.

The density is classified into two types as follows:

• Relative Density: The relative density is also known as specific gravity. It is defined as the ratio of the material’s density to the reference material’s density. It does not have units.

• Absolute Density: The mass of any substance per unit volume of a material is defined as absolute density. The unit of absolute density is g/cm³.

​Also Read: Specific Gravity Formula

The real-life applications of density include:

• Consider two balloons, one is filled with air while the other is filled with coke. Coke is much denser because its atoms move around less and take up less space. On the other hand, in an air balloon, the atoms collide with each other very quickly and therefore take up more space or less density. As a result, the balloon filled with air is light and the balloon filled with coke is heavy. 

• Life Tubes: The life tubes are found in swimming pools or beaches and are designed in such a way that they float in water and protect people from drowning while swimming. Life tubes float because they are filled with air which is less dense than water.
• Ships: Ships can float in water because they are designed with ballast tanks for holding air. These tanks offer large volumes with little mass which thereby decreases the ship’s density. When this reduced density is combined with the buoyant force it allows the ship to float over water.

​Also Check:

• Density is defined as the measurement of the mass of an object or body with a unit volume.
• The density of an object can be calculated by the formula: ρ = m/v
• Solids are denser than liquids and liquids are denser than gases.
• The density of water, i.e. 1 gram/cubic centimeter, is commonly used as the standard value for calculating the density of different substances.
• The CGS unit of density is gram per cubic centimeter (g/cm3).
• The density is classified into two types namely, absolute density and relative density.
• Life tubes and ships are two applications of the concept of density.

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