DensityCopy

Cheat Sheet: Density (O Level / IGCSE Physics)

1. Definition and Equation

• Density is defined as mass per unit volume
• Symbol: ρ (Greek letter “rho”)
• Equation:
  ρ = m / V
  where:
  ρ = density (kg/m³ or g/cm³)
  m = mass (kg or g)
  V = volume (m³ or cm³)
• Conversion:
  1 g/cm³ = 1000 kg/m³

2. Measuring Density

A. Density of a Liquid

Steps:

• Measure mass of empty measuring cylinder
• Pour known volume of liquid into it (read from meniscus)
• Measure mass of cylinder + liquid
• Calculate:
  mass of liquid = (mass of full cylinder) − (mass of empty cylinder)
  volume = from measuring cylinder
  density = mass / volume

B. Density of a Regularly Shaped Solid (e.g. cube, cylinder)

Steps:

• Measure length, width, height (or diameter & height for cylinder) using ruler/calipers
• Calculate volume using geometric formula
  • Cube/rectangular solid: V = length × width × height
  • Cylinder: V = πr²h
• Measure mass using electronic balance
• Calculate:
  density = mass / volume

C. Density of an Irregularly Shaped Solid (Displacement Method)

Steps:

• Measure mass of the object using balance
• Fill a measuring cylinder with water and note initial volume
• Gently lower the object into the water (must fully sink)
• Note final volume
• Calculate displaced volume:
  volume of object = final volume − initial volume
• Use:
  density = mass / displaced volume