Density and relative density are both measures of how tightly packed the particles of a substance are, but they are not the same.

- Density is the mass of an object per unit volume. It is measured in kilograms per cubic meter (kg/m³).

- Relative density is the density of a substance compared to the density of water at 4°C. It is dimensionless and is often expressed as a specific gravity.

For example, the density of iron is 7,874 kg/m³. This means that for every cubic meter of iron, there are 7,874 kilograms of iron. The relative density of iron is 7.87. This means that iron is 7.87 times denser than water.

The density and relative density of a substance can be used to determine its composition, purity, and other properties. For example, the density of a metal can be used to determine its purity. The relative density of a liquid can be used to determine its concentration.

Here is a table summarizing the key differences between density and relative density:

| Property | Density | Relative Density |

|---|---|---|

| Definition | Mass per unit volume | Density of a substance compared to the density of water at 4°C |

| Units | Kilograms per cubic meter (kg/m³) | Dimensionless |

| Formula | ρ = m/V | RD = ρ/ρ_water |

| Applications | Determining composition, purity, and other properties | Determining composition, concentration, and other properties |

Density and relative density are both important concepts in chemistry, physics, and engineering. They are used in a wide variety of applications, from determining the composition of materials to designing and building structures.