Weigh it, measure it, sink it. Then compare the two densities.
Density by two methods is one of the most common Question 1 experiments in IGCSE Physics Paper 6. Here a small metal block is weighed on a top-pan balance, its volume is found from its sides and then by displacement of water, and a displacement can deals with a stone too big for the cylinder. Watch the set-up built step by step, then build it yourself and check it against the points the examiners look for.
Past-paper referenceOriginal experiment, wording and figures, written in the style of Cambridge IGCSE Physics 0625 Paper 6 (Alternative to Practical). It is not copied from a past paper. The “what the examiners said” notes are our paraphrase of the Principal Examiner Reports for Teachers.
Practise next: 0625/63 October/November 2025, (volume of a block of modelling clay by measuring and by displacement on a thread) · official past papers
Practise next: 0625/63 May/June 2024, (density of modelling clay by two methods) · official past papers
Practise next: 0625/63 October/November 2023, (density of sand by two methods) · official past papers
Examiner reports used: 0625 March 2023, November 2023, June 2024, June 2025 (Papers 61 and 62) and November 2025.
This set-up builder needs JavaScript.
What a full-mark diagram shows
Mass
A top-pan balance, zeroed before the object goes on. If a dish is used, subtract its mass and show the working.
Volume from the sides
l, w and h with a ruler to the nearest mm (2.0 cm, not 2 cm), each measured in several places and averaged; V = l × w × h.
Volume by displacement
V1 and V2 read at eye level at the bottom of the meniscus; the object lowered gently on a thin thread until completely under water; V = V2 − V1.
Density and comparison
ρ = m / V to 2 or 3 significant figures with the unit g/cm³; the two values compared using a percentage difference against about 10%.
Habits the examiner reports keep asking for
Record to the resolution of the instrument: the nearest mm for a ruler, so 3.0 cm, never 3 cm.
Read the bottom of the meniscus, with your eye level with the water surface.
A source of inaccuracy must belong to the method, such as graduations too large for a small volume or the thread adding volume, with a matching improvement.
“Repeat” is not enough: say measure each side in several places and take the mean.
Always give a unit for density, g/cm³, and 2 or 3 significant figures.