Physics Theory : Density

Density is defined as the mass per unit volume of a substance.
∴ Density = Mass / Volume
The SI unit of density is kilogram/meter³ (kg/m³).
Another commonly used unit (CGS system) for density is g/cm³.
1 kg/m³ = 1000 g/m³ = (1000/1000000) g/cm³ = 1/1000 g/cm³.
So, divide by 1000 to convert from kg/m³ to g/cm³, and multiply by 1000 to convert from g/cm³ to kg/m³.

Density of water is about 1 g/cm³ or 1000 kg/m³ at room temperature.
Density of sea water (about 1.04 g/cm³ or 1040 kg/m³) is more than that of fresh water because of the salt dissolved in it.

Density of air is about 0.001 g/cm³ or 1 kg/m³ at room temperature and atmospheric pressure.

Approximate densities (in g/cm³) of some substances are given below.

• Tungsten (19.4)
• Mercury (13.6)
• Lead (11.4)
• Aluminum (2.7)
• Glass (2.2 to 2.7)
• Cork (0.05 to 0.1)

When a body floats, it displaces an amount of fluid equal to its own weight.