The shape of the lesson
By the end of the lesson, learners can
- Shrink the area, raise the pressure: Keep the force fixed and change the area it acts on.
- Points, blades, and snowshoes: The defining equation and its rearrangement for force:
- Equation: pressure = force ÷ area; unit pascal (Pa = N/m²).
- Resting object: the force is the weight, W = mg.
- Rearrange: area = force ÷ pressure.
One picture every idea returns to
Pressure is the force acting per unit area: p = F ÷ A, measured in pascals (Pa), where one pascal is one newton per square metre. For the same force, a smaller area gives a larger 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, The same force, spread thin.. A drawing pin barely needs a push to pierce a board, yet the same finger pressing flat does nothing. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Shrink the area, raise the pressure | Keep the force fixed and change the area it acts on. Project tab 1 of the lab (Pressure and applications) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Points, blades, and snowshoes | The defining equation and its rearrangement for force: Model the worked example Worked example on the board, one line at a time. | Round Table |
| 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 Points, blades, and snowshoes, 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.
Round Table
One sheet travels round the team. Each student adds one line of working or one idea and passes it on, so the solution is built four hands at a time and every contribution is visible.
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 |
|---|---|
| Two slips cost marks here. | First, divide the force by the area, do not multiply. Second, when an object simply rests on a surface, the force is its weight, so a mass in kilograms must be turned into a weight in newtons with W = mg before you divide. |
Pressure (p = F/A) and its applications: worksheet
6 questions, 13 marks. Written in the style of the papers; no past paper question is reproduced.
Define pressure, write the equation for it, and state its unit.
A force of 200 N acts on an area of 0.40 m². Calculate the pressure.
A crate of mass 12 kg rests on the floor on a face of area 0.60 m². Using g = 10 N/kg, calculate the pressure it exerts on the floor.
Explain why a sharp knife cuts more easily than a blunt one when pressed with the same force.
Explain why a heavy tractor is fitted with wide tyres so that it can drive over soft, muddy ground.
A force of 1000 N produces a pressure of 400 Pa on a surface. Calculate the contact area.
Answer key and marking notes
- Pressure is the force acting per unit area; p = F ÷ A. ✓
- Unit: pascal (Pa), where 1 Pa = 1 N/m². ✓
- p = F ÷ A = 200 ÷ 0.40
500 Pa
- weight W = mg = 12 × 10 = 120 N
p = F ÷ A = 120 ÷ 0.60
200 Pa
the force is the weight, not the mass
- A sharp blade has a much smaller contact area. ✓
- For the same force, p = F ÷ A gives a much higher pressure, so it cuts more easily. ✓
- Wide tyres give a large contact area. ✓
- For the tractor’s weight, a larger area gives a lower pressure, so it does not sink into the mud. ✓
- A = F ÷ p = 1000 ÷ 400
A = 2.5 m²
1 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 box exerts a force of 600 N on the floor through a contact area of 1.5 m². What is the pressure on the floor?
- A0.0025 Pa
- B400 Pa
- C598 Pa
- D900 Pa
Quiz key
p = F ÷ A = 600 ÷ 1.5 = 400 Pa. Option A inverts the formula; C subtracts; D multiplies.
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.