Explain density and relative density and write formulae.

Density
Definition: Density is the mass of a substance per unit volume. It describes how tightly the particles of a substance are packed together.
Formula:
Density(ρ)=Mass (m)Volume (V)\text{Density} (\rho) = \frac{\text{Mass (m)}}{\text{Volume (V)}}
Where:
• ρ\rho is the density in kg/m³ (SI unit).
• mm is the mass in kilograms (kg).
• VV is the volume in cubic meters (m³).
Relative Density
Definition: Relative density is the ratio of the density of a substance to the density of a reference substance (usually water for liquids and solids).
Formula:
Relative Density (R.D.)=Density of the substanceDensity of water\text{Relative Density (R.D.)} = \frac{\text{Density of the substance}}{\text{Density of water}}
Since relative density is a ratio, it has no unit (it is dimensionless).
For water:
• The density of water is 1000 kg/m31000 \, \text{kg/m}^3 (at standard conditions).
Relative density can also be expressed in terms of weights:
Relative Density=Weight of substanceWeight of an equal volume of water\text{Relative Density} = \frac{\text{Weight of substance}}{\text{Weight of an equal volume of water}}
Key Points
1. If relative density >1 > 1: The substance is denser than water and will sink in it.
2. If relative density <1 < 1: The substance is less dense than water and will float.