The shape of the lesson
By the end of the lesson, learners can
- Heat it, and feel the push: Change the temperature of a trapped gas and watch how the collisions, and so the pressure, change.
- Faster particles, harder hits: Every part of the behaviour follows from how often and how hard the particles strike the walls.
- Origin: particles collide with the walls and exert a force.
- Hotter: faster particles hit harder and more often.
- Smaller: particles reach the walls sooner, so they hit more often.
One picture every idea returns to
Gas pressure is caused by particles colliding with the walls of their container. Each collision pushes on the wall, and the force of these collisions per unit area is the pressure. Raising the temperature makes the particles move faster, so they hit the walls harder and more often, raising the pressure.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Pressure is a storm of collisions.. A balloon stays inflated because, every instant, millions of air molecules slam into its inner surface. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Heat it, and feel the push | Change the temperature of a trapped gas and watch how the collisions, and so the pressure, change. Project tab 3 of the lab (Gas pressure and temperature) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Faster particles, harder hits | Every part of the behaviour follows from how often and how hard the particles strike the walls. | Jigsaw |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 13 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Faster particles, harder hits, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Jigsaw
Split the content into expert pieces. Expert groups master one piece each, then regroup so every home team has one expert per piece, and each expert teaches their piece to the team.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Gas pressure is the result of particles striking the walls, not of the particles simply pressing against them while still. | When you heat a gas at constant volume, the pressure rises because the same particles collide with the walls more frequently and with greater force. |
Gas pressure and temperature: worksheet
6 questions, 13 marks. Written in the style of the papers; no past paper question is reproduced.
Explain, in terms of particles, how a gas exerts a pressure on the walls of its container.
A fixed mass of gas is sealed in a rigid container and then heated. Explain, in terms of the particles, why the pressure increases.
A gas is slowly compressed into a smaller volume while its temperature is kept constant. Explain why the pressure increases.
A student says that when a gas is heated at constant volume, the pressure rises because the particles get bigger and there are more of them. Explain what is wrong with this.
More gas is pumped into a sealed container of fixed volume, keeping the temperature the same. State and explain what happens to the pressure.
The pressure in a car tyre is found to be higher after a long, fast drive on a hot day than it was at the start. Explain why, in terms of the gas particles.
Answer key and marking notes
- The gas particles move and collide with the walls of the container. ✓
- Each collision exerts a small force on the wall; many collisions per unit area give the pressure. ✓
- Heating increases the temperature, so the particles move faster. ✓
- They strike the walls harder and more often (more collisions per second). ✓
- The greater force per unit area means a higher pressure. ✓
- In the smaller volume the particles have a shorter distance to travel before hitting a wall. ✓
- So they hit the walls more often, and the pressure increases. ✓
- The particles do not change size and their number does not change. ✓
- The pressure rises only because the particles move faster, so they hit the walls harder and more often. ✓
- The pressure increases. ✓
- There are now more particles, so there are more collisions with the walls each second. ✓
- The air in the tyre has warmed up, so its particles move faster. ✓
- They hit the inside walls of the tyre harder and more often, raising the pressure. ✓
2 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
A gas is held in a closed container. What causes the pressure that the gas exerts on the walls?
- AThe collisions of the gas particles with the walls.
- BThe weight of the gas pressing down.
- CThe particles sticking to the walls.
- DThe particles dissolving into the walls.
More gas is pumped into a sealed rigid container at constant temperature. Why does the pressure increase?
- AThere are more particles, so the walls are struck more frequently.
- BThe particles become larger.
- CThe particles move more slowly.
- DThe container shrinks.
Quiz key
Each particle that strikes a wall exerts a tiny force; the huge number of collisions per second produces the steady pressure. The weight of the gas (B) is negligible compared with this effect.
Adding gas means more particles in the same volume, so collisions with the walls happen more often and the pressure rises. At constant temperature the average particle speed is unchanged (ruling out C).
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.