Density is mass per unit volume, calculated as ρ = m/V. It measures how much matter is packed into a given space. Water has a density of 1 g/cm³ or 1000 kg/m³. Materials denser than their surrounding fluid sink; less dense materials float.

Understanding Density

Mass, Volume, and Buoyancy

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Density explains why a steel ship floats while a steel ball sinks, why hot air rises, and why oil floats on water. This fundamental property connects mass and volume, determining how materials behave in the physical world.

Common Material Densities

Material	Density (g/cm³)	Density (kg/m³)
Air (sea level)	0.0012	1.2
Cork	0.24	240
Wood (oak)	0.6-0.9	600-900
Ice	0.92	920
Water	1.00	1000
Aluminum	2.7	2700
Iron	7.87	7870
Gold	19.3	19300

Why Things Float or Sink

Archimedes' Principle

An object floats if its density is less than the fluid it's in:

Wood (0.7 g/cm³) floats in water (1.0 g/cm³)
Ice (0.92 g/cm³) floats in water
Oil (0.8-0.9 g/cm³) floats on water
Lead (11.3 g/cm³) sinks in water

Ships Float Because

Steel ships float because they enclose air, making their overall density less than water.

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Factors Affecting Density

Temperature: Most materials expand when heated, reducing density
Pressure: Gases compress significantly; solids and liquids much less
Composition: Alloys and mixtures have densities between their components

Conclusion

Density—mass per unit volume—is fundamental to understanding buoyancy, material properties, and physical behavior. Objects denser than their surrounding fluid sink; less dense objects float. This simple relationship explains phenomena from icebergs to hot air balloons.

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