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Science lesson plan · 3rd grade (Year 4 in England) · 45 minutes

Tug of war: add up forces and find the winner

Forces and motion

CCSS NGSS.3-PS2-1England: KS2 Y3 Forces and magnets

Objective and success criteria

Students will: Tug of war: add up forces and find the winner.

  • 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: Which way will it move? Predict from the forces

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 (Which way will it move? Predict from the forces). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. A rolling ball slows down and stops on grass. Which force caused this? (no force, it just ran out / a push from the ball / magnetism / friction from the grass) → friction from the grassPrompt: Something acted against the motion.
  2. True or false? Unbalanced forces can make an object start, stop, speed up or turn. (True / False) → TruePrompt: Compare the sizes and directions of the forces.
  3. True or false? A still object stays still if the forces on it are balanced. (True / False) → TruePrompt: Compare the sizes and directions of the forces.

Hook · 5 min

  • Drop a sheet of paper and a scrunched-up sheet together and ask why one falls faster.
  • Share the objective: Tug of war: add up forces and find the winner. 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: In a tug of war, the Red team's pullers pull with 80 N, 120 N, 80 N, 110 N. What is the Red team's total pull?
  • Step 1: 80 + 120 + 80 + 110 = 390
  • Step 2: So the answer is: 390 N
  • Answer: 390 N
  • 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. In a tug of war, the Red team's pullers pull with 120 N, 80 N, 100 N, 50 N. What is the Red team's total pull? → 350 NPrompt: Forces pulling the same way add together.
  2. Red team pulls left with 40 N, 50 N, 80 N. Blue team pulls right with 50 N, 80 N, 50 N. What is the size of the resultant (overall) force? → 10 NPrompt: Find each team's total first.

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. Red team pulls left with 40 N, 90 N, 100 N. Blue team pulls right with 100 N, 80 N, 100 N. What is the size of the resultant (overall) force? → 50 NPrompt: Find each team's total first.
  2. In a tug of war, the Red team's pullers pull with 80 N, 60 N. What is the Red team's total pull? → 140 NPrompt: Forces pulling the same way add together.

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: Which way will it move? Predict from the forces.
  • 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-3.

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

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Tug of war: add up forces and find the winner

Name

Date

Score/ 8

  1. Question 1

    In a tug of war, the Red team's pullers pull with 90 N, 110 N, 70 N, 100 N. What is the Red team's total pull?

    AnswerN

  2. Question 2

    Red team pulls left with 120 N, 40 N, 40 N. Blue team pulls right with 90 N, 110 N, 80 N. What is the size of the resultant (overall) force?

    AnswerN

  3. Question 3

    Red team (pulling left): 100 N + 40 N + 90 N. Blue team (pulling right): 120 N + 90 N + 70 N. What happens?

    230 N280 N
    • A. Red team wins (rope moves left)
    • B. nobody wins (balanced)
    • C. Blue team wins (rope moves right)

  4. Question 4

    In a tug of war, the Red team's pullers pull with 80 N, 40 N, 120 N. What is the Red team's total pull?

    AnswerN

  5. Question 5

    Red team pulls left with 40 N, 60 N, 90 N. Blue team pulls right with 110 N, 90 N, 40 N. What is the size of the resultant (overall) force?

    AnswerN

  6. Question 6

    Red team (pulling left): 100 N + 50 N + 110 N. Blue team (pulling right): 60 N + 50 N + 40 N. What happens?

    260 N150 N
    • A. Red team wins (rope moves left)
    • B. nobody wins (balanced)
    • C. Blue team wins (rope moves right)

  7. Question 7

    In a tug of war, the Red team's pullers pull with 90 N, 60 N, 90 N. What is the Red team's total pull?

    AnswerN

  8. Question 8

    Red team pulls left with 90 N, 50 N, 40 N. Blue team pulls right with 90 N, 80 N, 100 N. What is the size of the resultant (overall) force?

    AnswerN

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Answer key: Tug of war: add up forces and find the winner

  1. 1. 370 N

  2. 2. 80 N

  3. 3. C. Blue team wins (rope moves right)

  4. 4. 240 N

  5. 5. 50 N

  6. 6. A. Red team wins (rope moves left)

  7. 7. 240 N

  8. 8. 90 N