Science lesson plan · 7th grade (Year 8 in England) · 45 minutes
Pressure = force ÷ area
Forces and motion
CCSS NGSS.MS-PS2-2England: KS3 Physics: Motion and forces (pressure)England: GCSE Physics: Forces (pressure)
Objective and success criteria
Students will: Pressure = force ÷ area.
- I can answer questions on today's skill on my own, without help.
- I can explain each step and say why it works.
- I can check my answer and spot a mistake.
Before and after
Needs first: Mass and weight (W = mg)
Leads to: the next skill in this area.
Materials: Force meters, Toy cars and ramps, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).
Warm-up · 5 min
- Quick retrieval from earlier learning (Mass and weight (W = mg)). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- What is the weight of a 20 kg object on Earth? Use g = 9.8 N/kg. → 196 NPrompt: weight = mass × gravitational field strength (W = m g)
- An astronaut's mass is 80 kg. Gravitational field strength on the Moon is 1.6 N/kg. What would their weight be there, in N? → 128 NPrompt: Mass stays the same everywhere; weight changes.
- Mass and weight: which statement is NOT true? (You would weigh less on the Moon than on Earth. / Your mass is the same on the Moon as on Earth. / Mass is measured in kilograms. / Mass and weight are the same thing.) → Mass and weight are the same thing.Prompt: Which one changes on the Moon?
Hook · 5 min
- Drop a sheet of paper and a scrunched-up sheet together and ask why one falls faster.
- Share the objective: Pressure = force ÷ area. Read the success criteria together.
I do: model it · 10 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: A force of 40 N acts on an area of 2 m². What is the pressure, in pascals (Pa)?
- Step 1: 40 ÷ 2 = 20
- Step 2: So the answer is: 20 Pa
- Answer: 20 Pa
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 10 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- A force of 80 N acts on an area of 20 m². What is the pressure, in pascals (Pa)? → 4 PaPrompt: pressure = force ÷ area
- An elephant has a weight of 50000 N. The total area in contact with the ground is 0.5 m². What pressure is exerted on the ground, in Pa? → 100000 PaPrompt: The weight is the force pushing down.
You do: independent practice · 10 min
- Students work on the student sheet. Circulate and check the first two answers of every student early.
- Students who finish: write a question of their own for a partner, with the answer.
The 8 questions are on the student sheet below, with answers in the key.
Exit ticket · 5 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- Why does a sharp knife cut more easily than a blunt one? (The small edge area gives a much higher pressure for the same force / Sharp knives are magnetic / Sharp knives are heavier / Blunt knives have less friction) → The small edge area gives a much higher pressure for the same forcePrompt: Pressure = force ÷ area.
- A force of 200 N acts on an area of 20 m². What is the pressure, in pascals (Pa)? → 10 PaPrompt: pressure = force ÷ area
Watch out for
- Everyday meanings of words getting in the way of the science meaning: define key words explicitly.
- Remembering facts without the reason: ask "why?" and "what is the evidence?"
Support and stretch
Support
- Review first: Mass and weight (W = mg).
- Use concrete materials: force meters.
- Give the first step of each question, or a partly worked example to finish.
- Pair with a confident partner for the guided practice.
Stretch
- Explain a common mistake in writing and how to fix it.
- Write a word problem that uses today's skill, then solve a partner's.
Homework and more practice
Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-7.
Free lesson plan from eurekami.com/lesson-plan-builder