Density is mass per volume
Dense materials pack more mass into each unit of volume. Use mass and volume measurements with consistent units, and explain changes in density using particle spacing rather than saying particles themselves become heavier.
GCSE Physics resources
AQA GCSE Particle model of matter
Density and Particle Arrangement
Dense materials pack more mass into each unit of volume. Use mass and volume measurements with consistent units, and explain changes in density using particle spacing rather than saying particles themselves become heavier.
Start here
The quick revision snapshot
Dense materials pack more mass into each unit of volume. Use mass and volume measurements with consistent units, and explain changes in density using particle spacing rather than saying particles themselves become heavier.
By the end, you should be able to…
- Explain density is mass per volume 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 and Particle Arrangement. Read the model, use the visual, then test your recall before moving into examples and exam practice.
Build the picture
Density compares how much mass is packed into a volume. Heating usually makes particles move further apart; the particles do not grow. For a fixed mass, a larger volume gives a lower density, which explains why warm fluids can rise.
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
Choose a direct or displacement volume measurement, calculate ρ = m/V and compare values using the same units. 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 and particle packing
How does the same mass behave when the volume changes?
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
A block has mass 0.54 kg and dimensions 0.030 m × 0.020 m × 0.010 m. Calculate density.
- Find volume: 0.030 × 0.020 × 0.010 = 6.0 × 10⁻⁶ m³.
- Use ρ = m/V.
- Give kg/m³.
Show the answer
ρ = 0.54 ÷ 6.0 × 10⁻⁶ = 9.0 × 10⁴ kg/m³.
Example 2 · Displacement volume
Water rises from 40 cm³ to 65 cm³ when an irregular stone is submerged. Its mass is 75 g. Find density.
- Volume = 65 − 40 = 25 cm³.
- Use ρ = m/V.
- Keep g and cm³ together.
Show the answer
ρ = 75 ÷ 25 = 3.0 g/cm³.
Example 3 · Particle explanation
Explain why heating a liquid usually lowers its density.
- Keep mass fixed.
- State what heating changes.
- Link larger volume to density.
Show the answer
Particles move more and are on average farther apart, increasing volume. The same mass in a larger volume has lower density.
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.
- Mixing g/cm³ and kg/m³.
- Using final water volume instead of the rise.
- Saying particles expand.
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. State the SI unit of density.
[1 mark]Show answer and marking guidance
kg/m³.
2. A 200 g sample occupies 80 cm³. Calculate density in g/cm³.
[2 marks]Show answer and marking guidance
ρ = 200 ÷ 80 = 2.5 g/cm³.
3. Describe how to find the volume of an irregular solid.
[2 marks]Show answer and marking guidance
Submerge it in water and use the increase in volume, ensuring no air bubbles are trapped.
4. Explain why particles do not themselves get larger when heated.
[3 marks]Show answer and marking guidance
Heating increases their motion and average separation; it does not create larger particles.
5. A mass is unchanged but volume doubles. State what happens to density.
[2 marks]Show answer and marking guidance
Density halves because ρ = m/V.
6. Give one way to reduce uncertainty in a displacement measurement.
[1 mark]Show answer and marking guidance
Read the bottom of the meniscus at eye level and use a measuring cylinder with finer divisions.
Questions pupils ask
GCSE Physics FAQs
What is the key idea in Density and Particle Arrangement?
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 and Particle Arrangement?
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.