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Science lesson plan · 11th grade (Year 12 in England) · 60 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 · 6 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 5 kg object moving at 3 m/s, in kg m/s? → 15 kgm/sPrompt: momentum = mass × velocity
  2. An object of mass 2 kg has a momentum of 12 kg m/s. What is its velocity, in m/s? → 6 m/sPrompt: Rearrange p = m v.
  3. A lorry (truck) and a bicycle move at the same velocity. Which has more momentum? (the bicycle / the lorry (truck), because it has more mass / neither has momentum / they are equal) → the lorry (truck), because it has more massPrompt: Same v, different m.

Hook · 6 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 · 12 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 · 12 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 75 kg passenger moving at 10 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? → 7500 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 0.05 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.

You do: independent practice · 17 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 · 7 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. A 60 kg passenger moving at 12 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? → 1800 NPrompt: F = change in momentum ÷ time
  2. Why do cyclists' helmets contain crushable foam? (Foam reduces air resistance / Foam makes the helmet bounce / Crushing foam increases the time the head takes to stop / Foam is heavier than plastic) → Crushing foam increases the time the head takes to stopPrompt: Compare a hard landing with a soft one.

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/ 8

  1. Question 1

    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?

    Answer

  2. Question 2

    How do crumple zones in a car reduce injuries?

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

  3. Question 3

    A 75 kg passenger moving at 12 m/s is brought to rest in 0.05 s by a seat belt and airbag. What is the average force on the passenger, in N?

    AnswerN

  4. Question 4

    A helmet increases the time for a head to stop in a fall from 0.02 s to 0.2 s. The change in momentum is the same. By what factor is the average force reduced?

    Answer

  5. Question 5

    Why do cyclists' helmets contain crushable foam?

    • A. Crushing foam increases the time the head takes to stop
    • B. Foam makes the helmet bounce
    • C. Foam reduces air resistance
    • D. Foam is heavier than plastic

  6. Question 6

    A 80 kg passenger moving at 10 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

  7. Question 7

    A helmet increases the time for a head to stop in a fall from 0.05 s to 0.5 s. The change in momentum is the same. By what factor is the average force reduced?

    Answer

  8. Question 8

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

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

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

  1. 1. 10

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

  3. 3. 18000 N

  4. 4. 10

  5. 5. A. Crushing foam increases the time the head takes to stop

  6. 6. 8000 N

  7. 7. 10

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