GCSE Physics resources
AQA GCSE Particle model of matter
Gas pressure comes from repeated molecular impacts on a surface. Keep the amount of gas, volume and temperature conditions explicit before predicting a change.
Subsection scope: Molecular temperature/pressure is shared at both tiers. pV = constant is Physics only at both tiers; work on a gas is Physics Higher only.
Start here
Gas pressure comes from repeated molecular impacts on a surface. Keep the amount of gas, volume and temperature conditions explicit before predicting a change.
Before you revise
Choose an answer from memory. Your result tells you what to watch for in the guide.
Core revision guide
Gas pressure comes from repeated molecular impacts on a surface. Keep the amount of gas, volume and temperature conditions explicit before predicting a change.
Scope: 8463 and 8464 · Foundation and Higher
Gas molecules move randomly and collide with walls, exerting a force per unit area. Higher temperature means larger average kinetic energy. In the same volume, molecules strike the walls more frequently and with larger momentum changes; the average force and pressure rise. The container must remain sealed and rigid for this comparison.
Scope: 8463 Physics only · Foundation and Higher
For a fixed mass at constant temperature, p₁V₁ = p₂V₂. A smaller volume makes wall collisions more frequent while average kinetic energy remains unchanged. Doubling volume halves pressure. Pressures must be absolute rather than pressure above atmospheric pressure; the two volumes may use the same unit because their ratio is used.
Scope: 8463 Physics only · Higher only
Pushing a piston transfers energy mechanically into the enclosed gas. If the gas does not lose that energy by heating the surroundings, its internal energy and temperature can rise. This explains warming in a rapidly compressed bicycle pump. It is a different situation from slow compression held at constant temperature.
Misconception clinic
Read each belief, say what is wrong with it, then compare your correction.
Tempting idea: Its molecules become heavier.
Use instead: Molecular masses do not change. This raises the mean force per unit area.
Tempting idea: 50 kPa.
Use instead: Compression raises pressure. 100 × 60/30 = 200 kPa.
Retrieval practice
Explore the relationship
Use absolute temperature and volume to compare pressure with a gas at 20 °C and its starting volume.
Model scope: Optional enrichment: quantitative absolute-temperature/volume gas model; qualitative temperature–pressure reasoning is shared GCSE content
What to notice: use the readout to describe how one variable changes when the other is controlled.
Worked examples
Apply heating a rigid sealed container in the worked reasoning, then try the changed-context questions below.
Scope: 8463 and 8464 · Foundation and Higher
Faster particles collide with the walls more often and with greater force, so force per area and pressure increase.
Scope: 8463 Physics only · Foundation and Higher
In the smaller volume, particles hit the walls more often, increasing force per area and pressure.
Scope: 8463 Physics only · Foundation and Higher
Slower particles collide less often/less forcefully, so internal pressure falls and the balloon contracts until pressures balance.
Exam precision
Do this: State what stays fixed before explaining collisions or using pV. Distinguish constant-temperature compression from work that warms the gas.
Independent practice
Write an answer before opening the marking guidance. Then edit the exact phrase or step that would gain the next mark.
Scope: 8463 and 8464 · Foundation and Higher
Original PhysicsUK mark scheme: Point 1 (1 mark): Average molecular kinetic energy/speed increases. Point 2 (1 mark): Wall impacts become more frequent and involve larger momentum changes. Point 3 (1 mark): The average force per unit area and pressure increase. Award each distinct point once. Accept equivalent scientifically correct wording. No half marks.
Model answer: Faster molecules hit the walls more frequently with larger momentum changes, raising mean force per unit area.
Scope: 8463 Physics only · Foundation and Higher
Original PhysicsUK mark scheme: Point 1 (1 mark): p₁V₁ = p₂V₂. Point 2 (1 mark): p₂ = 120 × 80/50. Point 3 (1 mark): p₂ = 192 kPa. Award each distinct point once. Accept equivalent scientifically correct wording. No half marks.
Model answer: p₁V₁ = p₂V₂. p₂ = 120 × 80/50. p₂ = 192 kPa.
Acceptable answers: Expected result: p₂ = 192 kPa. Accept the unrounded value or a correctly rounded equivalent to two or more significant figures; accept equivalent units if converted correctly. No additional measurement interval is implied.
Marking notes: Method marks remain available after an arithmetic error. Carry an earlier numerical error into a later valid step; award that method point if the unit conversion and physics are correct. A fully correct answer with unit earns all marks unless working is expressly requested.
Questions pupils ask
Changing volume also changes collision frequency, so it would introduce a second cause of pressure change.
Useful next steps