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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 5 kg object on Earth? Use g = 9.8 N/kg. → 49 NPrompt: weight = mass × gravitational field strength (W = m g)
  2. An astronaut's mass is 60 kg. Gravitational field strength on the Moon is 1.6 N/kg. What would their weight be there, in N? → 96 NPrompt: Mass stays the same everywhere; weight changes.
  3. 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. / Weight is a force measured in newtons. / 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 40 N acts on an area of 2 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. A force of 100 N acts on an area of 20 m². What is the pressure, in pascals (Pa)? → 5 PaPrompt: pressure = force ÷ area
  2. Why do drawing pins have a wide head and a sharp point? (The wide head gives low pressure on your thumb; the point gives high pressure on the board / The head is magnetic / To make them look nice / To reduce the force needed) → The wide head gives low pressure on your thumb; the point gives high pressure on the boardPrompt: The same force acts on both ends.

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

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

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

  2. Question 2

    A force of 10 N acts on an area of 0.5 m². What is the pressure, in pascals (Pa)?

    AnswerPa

  3. Question 3

    A car has a weight of 12000 N. The total area in contact with the ground is 0.08 m². What pressure is exerted on the ground, in Pa?

    AnswerPa

  4. Question 4

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

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

  5. Question 5

    A force of 8 N acts on an area of 4 m². What is the pressure, in pascals (Pa)?

    AnswerPa

  6. Question 6

    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

  7. Question 7

    Why do snowshoes stop you sinking into deep snow?

    • A. They make you lighter
    • B. They spread your weight over a larger area, reducing pressure
    • C. They melt the snow
    • D. They increase the pressure

  8. Question 8

    A force of 200 N acts on an area of 20 m². What is the pressure, in pascals (Pa)?

    AnswerPa

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Answer key: Pressure = force ÷ area

  1. 1. C. Water pressure increases greatly with depth

  2. 2. 20 Pa

  3. 3. 150000 Pa

  4. 4. A. The wide head gives low pressure on your thumb; the point gives high pressure on the board

  5. 5. 2 Pa

  6. 6. 12000 Pa

  7. 7. B. They spread your weight over a larger area, reducing pressure

  8. 8. 10 Pa