Measuring density of regular and irregular objects
Measure mass with a balance. For a regular object, calculate volume from dimensions; for an irregular object, use water displacement. Read scales at eye level and remove trapped air bubbles.
GCSE Physics resources
AQA GCSE Particle model of matter
Density Required Practical
Measure mass with a balance. For a regular object, calculate volume from dimensions; for an irregular object, use water displacement. Read scales at eye level and remove trapped air bubbles.
Start here
The quick revision snapshot
Measure mass with a balance. For a regular object, calculate volume from dimensions; for an irregular object, use water displacement. Read scales at eye level and remove trapped air bubbles.
By the end, you should be able to…
- Explain measuring density of regular and irregular objects using precise physics language.
- Apply the relevant equations, diagrams or practical method to an exam-style situation.
- Use the mini quizzes and practice answers to identify and correct a misconception.
Core learning content
Learn the idea before you practise it
Start with this short teaching sequence for Density Required Practical. Read the model, use the visual, then test your recall before moving into examples and exam practice.
Build the picture
For a regular object, calculate volume from measured dimensions. For an irregular object, the rise in water level is its volume. Read the bottom of the meniscus at eye level, make sure the object is fully submerged and remove bubbles that would make the volume look too large.
Use the right relationship
Choose a relationship because of the physical change in the question, not because it is familiar. Density: ρ = m ÷ V (kg/m³, kg, m³). Specific heat capacity: E = mcΔθ (J, kg, J/(kg °C), °C). Pressure: p = F ÷ A (Pa, N, m²). Keep the unit next to each value while you substitute.
What a strong answer does
Give apparatus, measurements, equation, unit conversion, repeats and one uncertainty or validity improvement. Before writing, underline the command word and identify the information that matters. Keep a calculation as equation, substitution and answer with unit; keep an explanation as a linked chain using because, so or therefore. Finish by checking that the final sentence answers the exact context in the question and that the number, direction or conclusion agrees with the evidence given.
Retrieval practice
Quick checks
Answer without looking back first. The feedback explains the model, so a wrong answer still helps you learn.
Mini quiz 1
Check the core idea
Mini quiz 2
Apply the model
Mini quiz 3
Use exam precision
Try it
Density practical planner
Which measurements are needed before you calculate density?
What to notice: the readout and written explanation remain available if you do not use the controls.
Worked examples
See the method being built
Cover the answer, attempt the method and then compare your physics language as well as the number.
Example 1 · Regular-object method
Describe how to find the density of a metal cuboid.
- Measure mass with a balance.
- Measure length, width and height with a ruler/calipers.
- Calculate V then ρ = m/V.
Show the answer
Measure mass and dimensions, calculate volume = lwh, then divide mass by volume using consistent units.
Example 2 · Irregular-object method
Describe how to find density of an irregular stone.
- Measure mass on a balance.
- Record water-level increase when fully submerged.
- Use ρ = m/V.
Show the answer
The displaced-water volume equals the stone volume; divide its mass by this volume.
Example 3 · Spot a systematic issue
Air bubbles cling to a submerged object. Explain the effect.
- Bubbles increase apparent displacement.
- Apparent volume is too large.
- Use ρ = m/V.
Show the answer
The calculated density is too small because mass is divided by an overestimated volume.
Misconception clinic
Common wrong turns
Each of these is tempting because it sounds almost right. Replace it with the precise physics before you meet it in a question.
- Using centimetres and metres inconsistently.
- Forgetting to subtract initial water level.
- Not identifying the volume method for the object shape.
Independent practice
Exam-style questions
Use the working space first. Reveal the guidance only after you have committed to an answer, then improve the exact part that would gain the next mark.
1. Name the apparatus used to measure mass in the density practical.
[1 mark]Show answer and marking guidance
A balance.
2. State how to calculate the volume of a cuboid.
[1 mark]Show answer and marking guidance
Length × width × height.
3. State how to find an irregular object’s volume.
[1 mark]Show answer and marking guidance
Use the increase in water volume on submersion.
4. An object has mass 0.16 kg and volume 2.0 × 10⁻⁵ m³. Calculate density.
[2 marks]Show answer and marking guidance
ρ = 0.16 ÷ 2.0 × 10⁻⁵ = 8000 kg/m³.
5. Give one control/quality step for a displacement method.
[1 mark]Show answer and marking guidance
Ensure the object is fully submerged with no air bubbles and read at eye level.
6. Explain why repeated measurements of dimensions help.
[3 marks]Show answer and marking guidance
They reduce random uncertainty; a mean gives a more reliable volume.
Questions pupils ask
GCSE Physics FAQs
What is the key idea in Density Required Practical?
Use a particle model to explain density, changes of state, internal energy and gas pressure. Keep particle spacing, particle motion and energy separate.
How should I practise Density Required Practical?
Read the snapshot, attempt the worked examples without looking, complete the mini quizzes and then use the practice questions to check your wording and method.
Next step
Keep your revision moving
Physics sticks when you move between explanation, retrieval and application.