# What is Density? Density of various substances

### What is Density?

Density relates to the mass and weight of substances. This is so because equal volumes of different substance have got different masses and weights.

For instance; a box containing iron will be heavier (have a higher density) when compared to a similar box containing wood. This is true because wood has a lower density.

Similarly, a glass of water will have a higher density than an exact glass of oil. (Water has a higher density in this case). For this reason, oil floats on water.

The difference in the density of various substances is simply a result of the different atoms that make them up. For instance; water (H2O) is made up of hydrogen and oxygen atoms in the ratio of 2:1 and this is different from the constituent atoms making up common salt or sodiun chloride (NaCl). The constituent atoms in NaCl are sodiun and chlorine respectively.

• Density is defined as the mass of a unit volume of a material or substance.

The principle of density was determined by a Greek scientist named Archimedes.

The formula for density is shown below:

ρ = M/V

Where:

ρ = density

M= Mass

V = Volume

It is worthy of note to state that 'rho' is a Greek letter that expresses ρ (density).

The Standard International (SI) unit for density is kilogram per cubic metre (Kg/m3).

The table below shows various substances with their densities:

 Substance Density (Kg/m3) Helium 0.179 Air (1atm and 20oC) 1.20 Bamboo Wood 400 Ethanol 810 Methylated Spirit 800 Benzene 900 Paraffin Wax 900 Ice 920 Water (Fresh Water) 1000 Sea Water (Saline/Salt Water) 1030 1600 Glass 2600 Aluminium  (Al) 2700 Zinc (Zn) 7100 Iron (Fe) 7900 Copper (Cu) 8900 Lead (Pb) 11300 Mercury (Hg) 13600 19300 Platinum (Pt) 21500

Notice from the table that helium has a lower density than air and that's one reason why it's used in filling balloons.

Having an understanding on density offers a convenient means of deriving the mass of a body from its volume. Similarly, when we know the mass of a body, we can derive it's density.

Below are the derivation steps:

Mass = Volume x Density (M = Vρ)

Volume = Mass divided by the Density (V = M/ρ)

To get the weight of a body, we will need to multiply its mass by the acceleration of gravity.

A common application of density is seen in the way at which different materials interact with each other. For instance; a wood may float on water while an iron may sink in it.

Also, balloons will float in air because it's filled with helium gas which is much lighter (has a lower density) than air. Conversely, a nylon filled with sand will not float in air.