Lesson 8: Pressure, Force & Surface Area Calculations (P = F / A)
Exploring forces, net force calculations, motion graphs, energy, and real-world NZ physics applications.
🎯 Ngā Whāinga Akoranga | Learning Intentions
Pressure as force per unit area (P = F / A), units of pressure (Pascals Pa = N/m², N/cm²), and how spreading weight over large areas reduces pressure.
Calculate pressure P = F / A for objects standing on different surfaces (snowshoes vs high heels), convert areas, and explain real-world pressure applications.
🎥 Media Anchor & Pedagogical Scaffold
Pressure, Force & Area Physics Calculations
Video Clip: Pressure — the P = F ÷ A equation and why area changes how forces feel (Runtime: 4m 37s).
🧠 1. Before Viewing (Activate & Predict)
Why can an elephant walk safely on soft mud with large flat feet while a sharp high heel sinks immediately into the grass?
👁️ 2. During Viewing (Watch With a Job)
- Write the equation: state the pressure formula and identify the unit for pressure.
- Calculate: a force of 100 N acts on an area of 4 m². Calculate the pressure in Pa.
- Explain: why does a drawing pin hurt to press on but a flat hand does not — even with the same force? Use P = F/A.
🗣️ 3. After Viewing & Kaiako Move (Process & Apply)
Kaiako Move: Have students trace their shoes on grid paper to calculate total footprint area and estimate their standing pressure in Pa.
Immediate Task: Complete Worksheet 8: Pressure Calculation Problem Set & Footprint Area Investigation.
⚡ Whakaoho | Do Now: Same Person, Two Kinds of Shoe
Someone stands on soft ground in snowshoes, then in stiletto heels. Their weight has not changed by a single newton, yet one sinks and one does not.
Two minutes: write the word you think explains it, then write what you would have to measure to prove you are right.
📖 Activity 1: Calculate the Pressure, Then Mind the Units
Snowshoe against heel (13 min). Using P = F / A, find the pressure under each for the same person. Rough areas are fine — it is the ratio between them that matters, and the size of that ratio is genuinely surprising.
Convert carefully (12 min). Redo two calculations converting cm² to m² properly: divide by 10 000, not by 100. That single conversion is the most common error in this topic. Then work three real cases — tractor tyres, a drawing pin, a knife edge.
📝 Activity 2: Year 10 Physics Worksheet & Explanation Scaffolding (20 mins)
Logbook Section 8. Record: (1) both shoe calculations and the pressure ratio between them; (2) two conversions worked in full with the cm²-to-m² step visible; (3) three real applications, each saying whether the design raises or lowers pressure and why that is what the designer wanted.
🏫 Kaiako Planning & Pedagogy Notes
Year 10 Curriculum Alignment: NZ Curriculum Phase 4 Science — Physical World strand. Builds foundational physics problem-solving skills for NCEA Level 1 Mechanics and Level 2 Physics.