Density, mass, volume
ρ = m / V. Density triangle. Year 8 compound measure.
Density (g/cm³ or kg/m³) is mass per unit volume. Steel: ~7.85 g/cm³. Water: 1 g/cm³ (= 1000 kg/m³). Same triangle layout as speed-distance-time.
Worked examples
500 g of water has volume 500 cm³. ρwater = 1 g/cm³.
Iron block: 200 cm³ × 7.87 g/cm³ = 1574 g.
5 kg gold: V = 5000 g ÷ 19.3 g/cm³ ≈ 259 cm³.
Frequently asked questions
Why g/cm³ not kg/m³?
Same number for water (1 g/cm³ = 1000 kg/m³), but g/cm³ is the convenient lab-scale unit. SI uses kg/m³.
Float or sink?
An object floats in water if its density is less than 1 g/cm³.