| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Physics |
| Lesson Topic: Explain how molecular motion causes gas pressure and derive/use the relationship pV = (1/3) Nm⟨c²⟩, where ⟨c²⟩ is the mean‑square speed (one‑dimensional model extended to three dimensions) |
Learning Objective/s:
- Describe how molecular collisions with container walls generate pressure.
- Derive the one‑dimensional expression pV = N m⟨cₓ²⟩.
- Extend the derivation to three dimensions and obtain pV = (1/3) N m⟨c²⟩.
- Connect the kinetic‑theory result to the ideal‑gas law and temperature.
- Apply the formula to calculate gas pressure in a sample problem.
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Materials Needed:
- Projector and screen
- Whiteboard and markers
- Printed handout with key equations and example
- Calculator worksheets for the sample calculation
- PhET “Gas Properties” simulation (optional)
- Exit‑ticket slips
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Introduction:
Begin with a quick demonstration of a balloon inflating to highlight everyday pressure. Ask students what they think causes this pressure and link it to prior knowledge of the ideal‑gas law. State that by the end of the lesson they will be able to explain the microscopic origin of pressure and use the kinetic‑theory formula to solve quantitative problems.
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Lesson Structure:
- Do‑Now (5'): Students answer a short question – “If you double the temperature of a gas, what happens to the speed of its molecules?” Collect responses.
- Mini‑lecture (10'): Present the one‑dimensional model, derive pV = N m⟨cₓ²⟩ on the board, emphasising momentum change and collision frequency.
- Guided practice (8'): Work through the extension to three dimensions, showing isotropy and arriving at pV = (1/3) N m⟨c²⟩.
- Simulation & discussion (7'): Use the PhET gas simulation to visualise molecular collisions and relate observations to the derived formula.
- Example problem (10'): Students solve the nitrogen‑gas pressure calculation in pairs, using the handout worksheet.
- Check for Understanding (5'): Quick polling (show of hands) on the key steps of the derivation and its connection to the ideal‑gas law.
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Conclusion:
Summarise that gas pressure originates from molecular momentum transfer and that the kinetic‑theory expression links microscopic motion to macroscopic variables. Ask each student to write one‑sentence exit ticket answering: “How does temperature affect the average kinetic energy of gas molecules?” Assign homework to complete a worksheet converting between ⟨c²⟩, temperature, and pressure for different gases.
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