Physics · KS3 and GCSE · Interactive lesson
Density and pressure: comparing amounts
Explore mass per unit volume and force per unit area. Compare blocks and contact areas, then practise density and pressure calculations.
Choose your view
Explore an interactive example, then try the questions at your own pace.
KS3 / GCSE · start with the idea
By the end of this lesson: Compare the amount of mass packed into each unit of volume.
The interactive diagram and controls are in Stage 2, “Explore one example”. Read the idea here, then try it next.
- Density describes how much mass is packed into a volume.
- At the same volume, more mass means higher density.
- Compare both mass and volume, rather than judging by size alone.
Useful starting points
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What do the words mean?
- Mass
- How much matter is in an object; measured in g or kg.
- Volume
- The space occupied by an object; measured in cm³ or m³ here.
- Density
- Mass per unit volume, such as g/cm³ or kg/m³.
Change the example
This is the lesson example. Your practice question uses its own numbers.
Something to try
Keep the mass the same. Increase the volume. Is that mass more or less tightly packed?
Notice what changes
How particle motion works +
Starts paused. Press Play, then add energy to see the warmer particles move faster.
Particles keep the same size. Liquid particles move around; solid particles vibrate around fixed positions. This is a simplified model, with the change in motion exaggerated to make it easier to see.
About the playback +
About this model
Height shows volume; darker shading shows more mass. Shading is a diagram key, not a real material colour or a measure of density. The blocks have the same base area, and mass stays labelled above. Block A stays at 400 g and 200 cm³. This model compares uniform blocks, without predicting whether they float. ≈ marks a rounded density.
More about this diagram
Still picture. Play particle motion in Stage 2.
Block B’s density is the same as Block A’s.
Still picture of the example from Stage 2. Use the back arrow to change it.
Work through it
Starting example: read the steps below
- Block A has 400 g in 200 cm³.
- Block B has 400 g in 200 cm³.
- Hold volume steady first: more mass in the same space means greater density.
- Block B’s mass per volume is the same as Block A’s.
Try on your own
Your turn. No rush.
Question 1
Two blocks have the same volume. Block B has more mass. Which is denser?
About these questions
Questions appear in a mixed order. Work at your own pace and stop whenever you like.
These questions use their own numbers, separate from the lesson example. You can stop whenever you like. Answers last for this visit to the page.
A good place to pause
This recap is for the activity you just tried. You can return to other activities in this topic later.
Can you compare mass per volume and keep the density units consistent?
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Explain it in your own words and add a small example. This can help you remember and spot what to ask Maurice.
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Notes for parents and tutors
These lessons cover selected KS3 and GCSE ideas for England; they are not a complete course. The level notes explain where GCSE methods or optional extensions begin. Maurice can help you choose material for your course and exam board.
The content draws on the DfE Maths curriculum, DfE Science curriculum and AQA GCSE Physics specification. Level labels are guidance, not exam-board endorsements. For AQA Radioactivity, calculating net decline as a ratio is Higher-tier work. Net means the overall change; ask Maurice whether this extension is relevant to your course. Explanations and practice were reviewed during development on 21 October 2026; Maurice should check their fit before assigning work.
Topic labels and your lesson-view preference are saved in this browser. This tab also remembers the last lesson stage, so you can choose to continue there. If you choose revision, selected activities and suggested revisit dates are saved here too. Recent question codes are also kept to reduce repeats. Reflection notes are saved automatically per topic when you type them; you can delete a note in the recap. They stay in this browser and are visible to other people using it. Practice answers and enquiry details are not saved. Clearing browser data removes the labels.