Particle model
Lesson overview
This lesson introduces the core physics idea, the useful equipment and the calculation or data skills used on this page.
What you will learn
Pressure scenarios supplied on this page
Use the shoe, gas syringe, diver and floating object examples to practise pressure reasoning.
Gas pressure and pressure in fluids infographic
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. Increasing 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.
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.
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.
Exam-board guidance
Short board notes only. Learn the core physics above first.
AQA GCSE Physics
AQA GCSE Physics: often rewards clear physics explanations, correct equations, units and practical evidence for gas pressure, fluid pressure and pressure calculations.
OCR GCSE Physics
OCR GCSE Physics: often values precise definitions, clear working, graph interpretation and links between models and evidence.
Pearson Edexcel GCSE Physics
Pearson Edexcel GCSE Physics: often combines the concept with equation use, data handling and practical interpretation.
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: often expects accurate terms, units and evidence-based explanations using the shared physics idea.
CCEA GCSE Physics
CCEA GCSE Physics: connect the idea to your current unit and use the same practical method language your class uses.
Next lesson
Next, continue with Electromagnetic Spectrum Applications.