Particle model
This lesson builds gas pressure, fluid pressure and pressure calculations for GCSE Physics.
Use the core lesson first, then match the exam-board guidance to your school route. Many pupils meet this content through Combined Science as well as Separate Physics.
What you will learn
Exam-board fit
Exact paper labels and specification-point numbering vary by board and cohort, so match this lesson to your school route before using past-paper questions.
Pressure scenarios supplied on this page
Use the shoe, gas syringe, diver and floating object examples to practise pressure reasoning.
Clear explanation
Pressure is force spread over an area. The same force produces a larger pressure when it acts over a smaller area.
Gas pressure is caused by particles colliding with container walls. Higher temperature can make particles move faster, increasing collision rate and force if volume is fixed.
In liquids, pressure increases with depth because the weight of liquid above increases. This pressure acts in all directions.
Worked examples
Pressure from force and area
A force of 120 N acts over an area of 0.5 m2.
pressure = force ÷ area
pressure = 120 ÷ 0.5 = 240
Quick checks
Choose an answer, then check your thinking.
1. What happens to pressure if the same force acts over a smaller area?
2. What causes gas pressure inside a container?
Practice questions
Question 1
A force of 300 N acts on an area of 2 m2. Calculate pressure.
Reveal answer and marking guidance
Answer: 150 Pa.
Marking: Credit pressure = force ÷ area and 300 ÷ 2 = 150 Pa.
Question 2
Explain why a sharp knife cuts more easily than a blunt knife.
Reveal answer and marking guidance
Answer: The same force acts over a smaller area, producing a larger pressure.
Marking: Credit force over smaller area causing greater pressure.
Question 3
Why does water pressure increase with depth?
Reveal answer and marking guidance
Answer: There is more water above, so the weight of water pressing down is greater.
Marking: Credit greater depth and greater weight of liquid above.
Question 4
Why can heating a sealed gas increase its pressure?
Reveal answer and marking guidance
Answer: Particles move faster and collide with the walls more often and harder.
Marking: Credit faster particles and increased collisions with walls.
Exam practice ladder
Answers and marking guidance
The exact practice answers are hidden under each question so you can try first. For this lesson, marks come from using the correct physics model, choosing the right equation where needed, keeping units with values, and explaining changes with precise words such as transfer, resultant force, acceleration, evidence and uncertainty.
Common mistakes
- Multiplying force by area for pressure.
- Saying pressure only acts downwards in a liquid.
- Forgetting pascals or N/m2 as pressure units.
- Explaining gas pressure without particle collisions.
Exam-board guidance
All supported routes assess the core physics idea, but they may group topics, practicals and paper wording differently.
AQA GCSE Physics
AQA GCSE Physics: use this lesson for gas pressure, fluid pressure and pressure calculations, then check whether your class is taking Separate Physics or Combined Science.
OCR GCSE Physics
OCR GCSE Physics: the core physics idea is shared, but Gateway and Twenty First Century may organise questions differently.
Pearson Edexcel GCSE Physics
Pearson Edexcel GCSE Physics: practise the concept, the equation use and the practical language because questions often connect them.
Eduqas GCSE Physics
Eduqas GCSE Physics: learn the core explanation and practise applying it to unfamiliar contexts, data and practical questions.
WJEC Wales
WJEC Wales: check whether your class is using the current GCSE Physics route or a newer science route, then use this lesson for the shared physics idea.
CCEA GCSE Physics
CCEA GCSE Physics: connect the idea to your unit and remember that practical skills are assessed directly.
Extension challenge
Compare pressure from trainers and ice skates, then explain how the area changes the effect on ice.
Reveal answer
Example answer: A strong extension response names the physics model, uses accurate units and explains why the evidence supports the conclusion.
Next lesson
Next, continue with Electromagnetic Spectrum Applications.