Who this is for: Cambridge IGCSE Physics (0625) students who want Density — using ρ = m/V, predicting floating and sinking, and handling practical measurement questions — to become a reliable source of marks instead of a formula they apply without understanding.
What query it owns: how to understand and revise Density in Cambridge IGCSE Physics.
Why this is safe: this page owns the Density revision-guide angle, while Tutopiya’s Density subtopic page owns the learning resource and the free Density quiz owns the practice.

Density links mass and volume in Cambridge IGCSE Physics (0625) and appears in both calculation and practical questions. Whenever examiners give dimensions, a mass reading or a liquid-displacement setup, they expect you to use ρ = m/V, convert units carefully and compare densities to predict whether an object floats. This guide explains the core formula, the practical methods, the question types that actually appear, and where to practise each skill.

Key takeaways

• Density is mass per unit volume: ρ = m/V, with SI unit kg/m³ (or g/cm³ in some questions).
• An object floats if its density is less than the liquid; it sinks if density is greater.
• For irregular solids, find volume by displacement in a measuring cylinder.
• Always convert volume to m³ when using kg/m³, or keep g and cm³ together.

What is Density in Cambridge IGCSE Physics?

Density tells you how much mass is packed into each unit of volume. For a uniform substance, ρ = m/V. In Cambridge IGCSE Physics it is used to identify materials, compare whether objects float in water (density of water ≈ 1000 kg/m³ or 1.0 g/cm³), and in experimental questions where students measure mass with a balance and volume with a ruler or displacement can.

You can read the full explanation, worked examples and notes on Tutopiya’s Density subtopic page before you attempt questions.

The core ideas you must master

These four ideas appear again and again. Learn what each one means and the exam phrasing that signals it.

Idea	What it means	How the exam uses it
Density formula	ρ = m/V	”Calculate the density of the block”
Unit conversion	1 g/cm³ = 1000 kg/m³	”Give your answer in kg/m³”
Floating and sinking	Compare ρ_object with ρ_liquid	”State whether the object floats”
Displacement method	Volume = final − initial reading	”Describe how to find the volume of a stone”

How to calculate density — step by step

The safest method works for regular shapes, liquids and irregular solids.

1. Find mass m in kg (or g — stay consistent with volume units).
2. Find volume V — use length × width × height for regular blocks, or displacement for irregular objects.
3. Write ρ = m/V and substitute.
4. Include the correct unit — kg/m³ or g/cm³ as requested.
5. For floating questions, compare your density with the liquid’s density.

Once you have worked through a few, test yourself with the free Density quiz — it tells you fast whether the method has actually stuck.

Regular vs irregular objects: which method does the question want?

Students lose marks by using the wrong volume method or mixing unit systems.

Situation	What to do	Typical signal words
Cuboid or cylinder	Calculate volume from dimensions	”length 10 cm, width 5 cm, height 2 cm”
Irregular solid	Displacement in measuring cylinder	”stone”, “describe an experiment”
Liquid	Volume from cylinder reading	”measuring cylinder contains 50 cm³”
Float or sink	Compare densities only	”density of water is 1000 kg/m³”

Density in past-paper wording: command words that matter

Most lost marks come from unit errors or comparing density with mass instead of with the liquid’s density.

Command word / phrase	What the question wants	Typical Density stem
Calculate / Work out	Use ρ = m/V with full working	”Work out the density of the metal.”
Describe	Practical method for volume	”Describe how to measure the density of a small stone.”
State	Float/sink decision with reason	”State whether the block floats. Explain.”
Suggest	Identify a material from density	”Suggest what the object is made of.”
Give your answer in …	Convert to required unit	”Give your answer in kg/m³.”

Worked exam-style stems (how to answer the wording)

Practising the wording — not just the formula — is what method marks reward. Here is how three real-style stems are answered.

1. “A block has mass 200 g and volume 50 cm³. Calculate its density in g/cm³.” ρ = m/V = 200/50 = 4.0 g/cm³. Mark-scheme reward: formula, substitution, unit.
2. “The density of water is 1000 kg/m³. A wooden block has density 600 kg/m³. State whether it floats.” The block is less dense than water, so it floats. Reward: correct comparison linked to floating.
3. “Describe how to find the density of an irregular stone.” Find mass on a balance. Submerge stone in water in a measuring cylinder; volume = rise in reading. Calculate ρ = m/V. Reward: both mass and displacement steps.

When you can recognise the wording instantly, work the full set on the Motion, Forces and Energy topical past-paper questions and the Density quiz to lock the method in.

How Density connects to the rest of Motion, Forces and Energy

Density feeds into Pressure in liquids (P = ρgh) and relies on accurate Mass and Weight measurements. It also links to the particle model in Kinetic Particle Model of Matter, where denser materials have particles closer together. When you are ready to move on, the Cambridge IGCSE Physics resource hub lets you jump straight from a weak subtopic into the next.

Common mistakes students make

• Mixing g with m³ or kg with cm³ without converting.
• Forgetting that 1 g/cm³ = 1000 kg/m³.
• Saying an object floats because it is light rather than less dense than the liquid.
• Using total cylinder reading instead of the change in volume for displacement.
• Rounding too early in multi-step density calculations.

When you need more support

If Density questions keep tripping you up — especially unit conversion or displacement practicals — work through the Motion, Forces and Energy topical past-paper questions and the Density quiz to pinpoint the exact gap, then get focused help from a Cambridge IGCSE Physics tutor to fix it quickly.

Frequently asked questions

Is Density hard in Cambridge IGCSE Physics? No — the formula is simple. Marks are lost on unit conversion, wrong volume methods and weak explanations of floating.

What is the density of water in IGCSE Physics? Use 1000 kg/m³ or 1.0 g/cm³ unless the question states otherwise.

How do you find the volume of an irregular object? Use the displacement method: note the measuring-cylinder reading before and after submerging the object; the difference is the volume.

How do I revise Density effectively? Read the subtopic notes, practise both calculation and describe-style questions, then take the Density quiz. Revisit any unit-conversion errors before moving on.

Ready to master Cambridge IGCSE Physics Density?

Start with the Density subtopic page, then book a free trial with a Cambridge IGCSE Physics specialist to turn Density into guaranteed marks.

Ready to Excel in Your Studies?

Get personalised help from Tutopiya's expert tutors. Whether it's IGCSE, IB, A-Levels, or any other curriculum — we match you with the perfect tutor and your first session is free.

Book Your Free Trial