##  [Density](/density-0) 

 Definition

Mass per unit volume of a substance, commonly expressed in kilograms per cubic metre (kg·m⁻³) or grams per cubic centimetre (g·cm⁻³).

 

 

 

 

 

 





## Principle

Principle

Density is an intensive property defined as ρ = m/V for a homogeneous sample; it depends on composition, temperature, and pressure for compressible phases and can indicate structural or compositional differences.

 

 

 

 

 





## Demonstration

Demonstration

Pure water at 4 °C has a density near 1.000 g·cm⁻³ (1000 kg·m⁻³); measuring mass of a known-volume sample yields density, which can distinguish between ethanol (0.789 g·cm⁻³) and octane (0.703 g·cm⁻³).

 

 

 

 

## Misapplication

Misapplication

Treating density as a fixed intrinsic constant without specifying temperature and pressure, or averaging densities of heterogeneous mixtures without accounting for porosity or trapped voids.

 

 

 

 

 





## Consequence

Consequence

Accurate density values allow conversion between mass and volume, support buoyancy and fluid dynamics calculations, and serve as a diagnostic for purity, phase, or composition in materials analysis.

 

 

 

 

## Reversal

Reversal

Specific volume (the reciprocal of density) emphasizes the volume per unit mass; while density compresses information into mass per volume, specific volume is preferred in some thermodynamic treatments.

 

 

 

 

 





## Boundary

Boundary

Applies to bulk homogeneous phases or well-defined samples at specified state conditions; excludes anisotropic apparent densities (e.g., packing density of powders), effective densities in porous or composite materials without qualification, and pointwise mass distributions in inhomogeneous fields.

 

 

 

 

 





## Semantic Tension

Semantic Tension

Tension between 'density' as an easily measured laboratory property and its dependence on state variables and microstructure leads to ambiguity when temperature, pressure, porosity, or composition are omitted.

 

 

 

 

 





## Synthesis

Synthesis

Density is the intensive property mass per unit volume for a homogeneous sample under specified conditions; it converts between mass and volume, informs buoyancy and material identification, and must be reported with state information to be useful.