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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.
  1. What is the weight of a 35 kg object on Earth? Use g = 9.8 N/kg. → 343 NPrompt: weight = mass × gravitational field strength (W = m g)
  2. An astronaut's mass is 20 kg. Gravitational field strength on Jupiter is 25 N/kg. What would their weight be there, in N? → 500 NPrompt: Mass stays the same everywhere; weight changes.
  3. Mass and weight: which statement is NOT true? (Mass is measured in kilograms. / Weight is a force measured in newtons. / Your mass is the same on the Moon as on Earth. / 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.
  1. A force of 100 N acts on an area of 5 m². What is the pressure, in pascals (Pa)? → 20 PaPrompt: pressure = force ÷ area
  2. A car has a weight of 12000 N. The total area in contact with the ground is 0.1 m². What pressure is exerted on the ground, in Pa? → 120000 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.
  1. Why do snowshoes stop you sinking into deep snow? (They make you lighter / They spread your weight over a larger area, reducing pressure / They increase the pressure / They melt the snow) → They spread your weight over a larger area, reducing pressurePrompt: Same force, bigger area.
  2. An elephant has a weight of 50000 N. The total area in contact with the ground is 0.25 m². What pressure is exerted on the ground, in Pa? → 200000 PaPrompt: The weight is the force pushing down.

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

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Pressure = force ÷ area

Name

Date

Score/ 8

  1. Question 1

    A force of 1 N acts on an area of 0.5 m². What is the pressure, in pascals (Pa)?

    AnswerPa

  2. Question 2

    Why do drawing pins have a wide head and a sharp point?

    • A. To reduce the force needed
    • B. The wide head gives low pressure on your thumb; the point gives high pressure on the board
    • C. The head is magnetic
    • D. To make them look nice

  3. Question 3

    A walker has a weight of 600 N. The total area in contact with the ground is 0.05 m². What pressure is exerted on the ground, in Pa?

    AnswerPa

  4. Question 4

    A force of 100 N acts on an area of 5 m². What is the pressure, in pascals (Pa)?

    AnswerPa

  5. Question 5

    Why are deep-sea submersibles built with very thick walls?

    • A. Water pressure increases greatly with depth
    • B. There is no pressure deep down
    • C. To make them float
    • D. Deep water is hotter

  6. Question 6

    A car has a weight of 12000 N. The total area in contact with the ground is 0.1 m². What pressure is exerted on the ground, in Pa?

    AnswerPa

  7. Question 7

    A force of 80 N acts on an area of 20 m². What is the pressure, in pascals (Pa)?

    AnswerPa

  8. Question 8

    Why does a sharp knife cut more easily than a blunt one?

    • A. Sharp knives are heavier
    • B. The small edge area gives a much higher pressure for the same force
    • C. Sharp knives are magnetic
    • D. Blunt knives have less friction

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Answer key: Pressure = force ÷ area

  1. 1. 2 Pa

  2. 2. B. The wide head gives low pressure on your thumb; the point gives high pressure on the board

  3. 3. 12000 Pa

  4. 4. 20 Pa

  5. 5. A. Water pressure increases greatly with depth

  6. 6. 120000 Pa

  7. 7. 4 Pa

  8. 8. B. The small edge area gives a much higher pressure for the same force