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Science lesson plan · 11th grade (Year 12 in England) · 30 minutes

Force and rate of change of momentum (safety design)

Forces and motion

CCSS NGSS.HS-PS2-3CCSS NGSS.HS-ETS1-2England: GCSE Combined Science: Forces (Physics only: changes in momentum)

Objective and success criteria

Students will: Force and rate of change of momentum (safety design).

  • 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: Momentum (p = m v)

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 · 4 min

  • Quick retrieval from earlier learning (Momentum (p = m v)). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. What is the momentum of a 0.5 kg object moving at 3 m/s, in kg m/s? → 1.5 kgm/sPrompt: momentum = mass × velocity
  2. An object of mass 0.2 kg has a momentum of 5 kg m/s. What is its velocity, in m/s? → 25 m/sPrompt: Rearrange p = m v.
  3. A lorry (truck) and a bicycle move at the same velocity. Which has more momentum? (neither has momentum / the bicycle / they are equal / the lorry (truck), because it has more mass) → the lorry (truck), because it has more massPrompt: Same v, different m.

Hook · 3 min

  • Drop a sheet of paper and a scrunched-up sheet together and ask why one falls faster.
  • Share the objective: Force and rate of change of momentum (safety design). Read the success criteria together.

I do: model it · 7 min

  • Work through the example out loud, saying why you do each step, not just what you do.
  • Example: A 80 kg passenger moving at 15 m/s is brought to rest in 0.4 s by a seat belt and airbag. What is the average force on the passenger, in N?
  • Step 1: Δp = 80 × 15 = 1200 kg m/s
  • Step 2: F = 1200 ÷ 0.4 = 3000
  • Step 3: So the answer is: 3000 N
  • Answer: 3000 N
  • Pause after each step and ask a student to say what comes next.

We do: guided practice · 6 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 60 kg passenger moving at 12 m/s is brought to rest in 0.2 s by a seat belt and airbag. What is the average force on the passenger, in N? → 3600 NPrompt: F = change in momentum ÷ time
  2. A helmet increases the time for a head to stop in a fall from 0.01 s to 0.1 s. The change in momentum is the same. By what factor is the average force reduced? → 10Prompt: F = Δp ÷ t, so force is inversely proportional to time.

You do: independent practice · 7 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 6 questions are on the student sheet below, with answers in the key.

Exit ticket · 3 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. Why do gymnasts land on thick soft mats? (The mat increases stopping time, reducing the force on their legs / The mat reduces their mass / Mats bounce them higher / The mat increases their speed) → The mat increases stopping time, reducing the force on their legsPrompt: The change in momentum is fixed.
  2. A helmet increases the time for a head to stop in a fall from 0.02 s to 0.1 s. The change in momentum is the same. By what factor is the average force reduced? → 5Prompt: F = Δp ÷ t, so force is inversely proportional to time.

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: Momentum (p = m v).
  • 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-11.

Free lesson plan from eurekami.com/lesson-plan-builder

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Force and rate of change of momentum (safety design)

Name

Date

Score/ 6

  1. Question 1

    Why do cricket or baseball fielders pull their hands back as they catch a fast ball?

    • A. It increases the ball's speed
    • B. It makes the ball lighter
    • C. It increases the time to stop the ball, reducing the force on their hands
    • D. It changes the ball's momentum to zero instantly

  2. Question 2

    A 60 kg passenger moving at 20 m/s is brought to rest in 0.2 s by a seat belt and airbag. What is the average force on the passenger, in N?

    AnswerN

  3. Question 3

    A helmet increases the time for a head to stop in a fall from 0.02 s to 0.1 s. The change in momentum is the same. By what factor is the average force reduced?

    Answer

  4. Question 4

    How do crumple zones in a car reduce injuries?

    • A. They reduce the change in momentum to zero
    • B. They stop the car instantly
    • C. They make the car heavier
    • D. They increase the time taken to stop, so the force on passengers is smaller

  5. Question 5

    A 75 kg passenger moving at 20 m/s is brought to rest in 0.1 s by a seat belt and airbag. What is the average force on the passenger, in N?

    AnswerN

  6. Question 6

    A helmet increases the time for a head to stop in a fall from 0.01 s to 0.04 s. The change in momentum is the same. By what factor is the average force reduced?

    Answer

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Answer key: Force and rate of change of momentum (safety design)

  1. 1. C. It increases the time to stop the ball, reducing the force on their hands

  2. 2. 6000 N

  3. 3. 5

  4. 4. D. They increase the time taken to stop, so the force on passengers is smaller

  5. 5. 15000 N

  6. 6. 4