Physics · KS3 and GCSE · Interactive lesson
Gas pressure: particles, volume and temperature
Watch a sealed gas in a particle model. Change space or temperature, explain wall collisions and build towards GCSE pressure–volume 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: Explain how changing the space for a fixed gas amount changes its pressure.
The interactive diagram and controls are in Stage 2, “Explore one example”. Read the idea here, then try it next.
- Gas particles are already moving in different directions.
- Their collisions with the container walls produce pressure.
- Change one thing at a time: the space available or the temperature.
Useful starting points
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What do the words mean?
- Pressure
- Force per unit area on a surface.
- Pascal (Pa)
- A unit of pressure. One kilopascal (1 kPa) is 1,000 Pa.
- Absolute pressure
- Pressure measured from a vacuum, where pressure is zero. A tyre gauge usually shows pressure above the surrounding air pressure instead.
- Volume
- The space available to the gas.
- Collision
- A particle hitting a wall or another particle.
- Kinetic energy
- Energy associated with movement.
- Sealed
- No gas particles enter or leave.
Change the example
This is the lesson example. Your practice question uses its own numbers.
Something to try
Play the motion. Halve the volume while temperature stays fixed. Why do the particles hit the walls more often?
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
A simplified ideal gas, shown in a 2D slice. Twenty dots represent a fixed amount of gas, not twenty real molecules; particle sizes and time are not to scale. Wall bounces are illustrated; collisions between particles are omitted. Volume changes with container width at fixed cross-section. Animation speed scales with the square root of absolute temperature, so 20 °C to 100 °C gives a modest speed change, not five times the speed. Pressure is absolute pressure, not a tyre gauge reading.
More about this diagram
Still picture. Play particle motion in Stage 2.
Pressure = 100 kPa
Still picture of the example from Stage 2. Use the back arrow to change it.
Work through it
Starting example: read the steps below
- Start with sealed gas at 100 cm³ and 20 °C.
- Keep its temperature at 20 °C while changing volume to 100 cm³.
- The space available is unchanged.
- The pressure is unchanged. The particles themselves stay the same size.
Try on your own
Your turn. No rush.
Question 1
What produces pressure on a gas container’s walls?
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
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Can you explain pressure using wall collisions and say what was kept fixed?
Try one question and explain your first step. If you need help, use a hint, go back to the idea, or ask Maurice. You choose the pace.
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.
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