1) Density or Mass density (ρ) – mass per unit volume is called density.
ρ= mass/volume
If density increases, so mass increases , so structure is compact or dense medium. If density decreases mass decreases.
SI unit of density is kg/m³
Note: Density of water is maximum at 4°C. Density of water at 4°C is 1000 kg/m³
2) Weight density– It is called weight per unit volume.
Weight density= Weight(W)/Volume(V) = N/m³
Weight density= ρ*g where ρ is mass density and g is gravitational acceleration.
3) Specific Gravity or Relative Density- Specific Gravity= Density of fluid / Density of standard fluid at STP
For liquid- Specific Gravity= Density of liquid/ Density of water at 4°C
For gas- Specific Gravity= Density of gas/ Density of air at STP
Note: 1) Density of water at 4°C is 1000 kg/m³ 2) Density of air at STP is 1.21 kg/m³
Mechsiast 