Newton's Third Law

Do Now: Anagram Challenge

GTT: Activating Hard Thinking Retrieval Practice

Why This Matters

Retrieving the names of forces from memory strengthens your recall. Unscramble each anagram to reveal a type of force — you've met all of these before!

GIEHTW

FILT

GARD

STTURH

TNICRIOF

STURUPTH

RIA ANETCSISRE

SUPH

Recap: Newton's First & Second Laws

GTT: Structuring Spaced Retrieval

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Think (1 min)

Can you recall Newton's First and Second Laws without looking at your notes?

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Pair (2 mins)

Compare with a partner. Fill in any gaps in each other's recall.

Complete Newton's Laws using the word bank:

Word Bank

constant velocityrestexternal forceaccelerationmassF = m × a

Newton's First Law:

An object at or moving at a will remain like this unless an acts upon it.

Newton's Second Law:

The of an object depends on the size of the force applied and the object's .

The equation is:

Write out both laws from memory, then answer:

Newton's First Law:

Newton's Second Law:

Apply: A 1500 kg car accelerates at 2 m/s². Calculate the resultant force.

Recall and extend:

1. Write both laws from memory:

2. A 60 kg skydiver falls with weight 600 N and air resistance 400 N. Calculate the resultant force and acceleration.

3. How do the First and Second Laws link together? Explain what happens when resultant force is zero vs non-zero.

First Law: An object at rest or moving at a constant velocity will remain like this unless an external force acts upon it.

Second Law: The acceleration of an object depends on the size of the force applied and the object's mass. F = m × a

Core apply: F = 1500 × 2 = 3000 N

Challenge: Resultant = 600 − 400 = 200 N downwards. a = 200 / 60 = 3.33 m/s²

Teacher-Led GTT: Understanding Content Dual Coding

📚 Newton's Third Law of Motion

"For every action, there is an equal and opposite reaction."

The pair of forces acting upon objects are called action-reaction forces.

The two forces are always the same size and act in opposite directions.

Three Key Rules

1. Action and reaction forces are equal in size

2. They act in opposite directions

3. They act on different objects

The Dog and Rope Model

ACTION

🐕 Dog

🪢 Rope

🧑 Person

REACTION

Dog pulls rope LEFT → Rope pulls dog RIGHT (different objects!)

Person pulls rope RIGHT → Rope pulls person LEFT (different objects!)

🇦🇪 UAE Connection: The Hope Mars Mission

The UAE's Hope Probe launched in 2020 using Newton's Third Law. The rocket engines expelled hot gases downwards (action) and the gases pushed the rocket upwards (reaction). These forces acted on different objects — the gases and the rocket.

Use the keywords below to explain Newton's Third Law:

Keywords

actionreactionequaloppositedifferent objectsforce pair

Sentence starter: "Newton's Third Law states that for every _______ there is an _______ and _______ _______. These forces act on _______ _______."

Write your answer:

Explain Newton's Third Law in your own words:

Your explanation (must include: "equal", "opposite", "different objects"):

Give one real-world example of an action-reaction pair:

Explain how Newton's Third Law enables rocket propulsion:

Explain (3 marks — state the law, identify both forces, name both objects):

Why does the rocket accelerate upwards even though the action and reaction forces are equal?

Balanced Forces vs Action-Reaction Pairs

Teacher-Led GTT: Structuring Concrete Examples

📚 This Is the Key Distinction

Balanced Forces

Act on the SAME object

Equal and opposite

Object doesn't accelerate

Example: Weight ↓ and Reaction ↑ on a book

Action-Reaction Pairs

Act on DIFFERENT objects

Equal and opposite

Always exist — even when moving

Example: Hand pushes wall / Wall pushes hand

⚠️ Common Misconception

"A book on a table: weight down and reaction up is Newton's Third Law."

✓ This is BALANCED FORCES — both act on the same object (the book).

✓ The 3rd Law pair for the book's weight is: Earth pulls book down / Book pulls Earth up (different objects!).

Sort each example: Balanced Forces or Action-Reaction Pair?

Remember

Ask yourself: "Do both forces act on the SAME object or DIFFERENT objects?"

Same object = Balanced | Different objects = Action-Reaction

Example	Balanced or Action-Reaction?
A book resting on a table (weight down, reaction up — both on the book)
Earth pulls apple down / Apple pulls Earth up
A person leaning on a wall: hand pushes wall / wall pushes hand
A plane flying at constant speed (thrust = drag, both on the plane)
Swimmer pushes water backwards / Water pushes swimmer forwards

For each example, state whether it is balanced forces or an action-reaction pair. Explain your reasoning.

a) A book resting on a table — weight acting down, reaction force acting up:

b) You push a shopping trolley forward / The trolley pushes back on your hands:

c) A fish swimming at constant speed — forward force and drag are equal:

d) The Moon orbiting Earth — Earth pulls Moon / Moon pulls Earth:

Evaluate these student statements:

Student A says: "A book on a table doesn't move because the action and reaction forces cancel out."

Evaluate this statement. Is the student correct? Explain fully. (4 marks)

Student B says: "If action and reaction forces are equal and opposite, nothing should ever move."

Evaluate this statement. Explain why objects CAN move despite Newton's Third Law. (4 marks)

Foundation sorting: Balanced | Action-Reaction | Action-Reaction | Balanced | Action-Reaction

Challenge — Student A: Incorrect. The book doesn't move because the forces are balanced (both act on the book). Weight down and reaction up are NOT a Newton's 3rd Law pair — they act on the same object.

Challenge — Student B: Incorrect. Action-reaction forces act on different objects, so they cannot cancel each other out. Movement depends on the resultant force on one object. E.g. a rocket: the thrust acts on the rocket while the equal force acts on the exhaust gases.

Action-Reaction Scenarios

GTT: Maximising Opportunity Deliberate Practice

Remember the Rule

For each scenario, state the reaction force. Your answer must name both objects and show the forces are equal, opposite, and on different objects.

State the reaction force for each action:

Sentence Frame

"If [Object A] exerts a force on [Object B], then [Object B] exerts an equal and opposite force on [Object A]."

1. 📚 A student picks up a book (exerts an upward force on the book).

Reaction: The exerts an equal force on the .

2. 🌍 The Earth exerts a gravitational force on the Moon.

Reaction: The exerts an equal gravitational force on the .

3. 🐒 A monkey hangs from a branch (exerts a downward force on the branch).

Reaction: The exerts an equal force on the .

4. 🐎 A horse pushes the ground backwards as it gallops.

Reaction: The pushes the .

For each scenario, write the full action-reaction pair. Name both objects and both force directions.

1. A student picks up a book:

2. The Earth exerts a gravitational force on the Moon:

3. A monkey hangs from a branch:

4. A horse gallops along the ground:

5. A swimmer pushes water backwards with their hands:

Extended contexts — explain the action-reaction pairs AND link to motion:

1. A rocket launches from Earth. Explain, using Newton's Third Law, how this occurs. (3 marks)

2. A runner sprints along a track. Explain, using Newton's Third Law, how the runner moves forward. (3 marks)

3. The Moon orbits the Earth. Explain the 3rd Law pair and why the Moon moves more than the Earth. (4 marks)

4. Why do astronauts push gently when moving inside a spacecraft? (2 marks)

1. Student & book: Action: Student exerts upward force on book. Reaction: Book exerts equal downward force on student's hand.

2. Earth & Moon: Action: Earth pulls Moon towards it. Reaction: Moon pulls Earth towards it with an equal gravitational force.

3. Monkey & branch: Action: Monkey pulls branch down. Reaction: Branch pulls monkey up.

4. Horse & ground: Action: Horse pushes ground backwards. Reaction: Ground pushes horse forwards.

5. Swimmer: Action: Swimmer pushes water backwards. Reaction: Water pushes swimmer forwards.

Challenge 3 (Moon): The forces are equal (3rd Law), but the Earth has much greater mass, so by F = ma its acceleration is tiny. The Moon, with less mass, accelerates more noticeably — which is why it orbits the Earth.

Challenge 4 (Astronauts): Minimal friction in a spacecraft means even a small reaction force causes noticeable acceleration (F = ma with small mass relative to force).

The Leaning Wall Task

Live Modelling GTT: Explaining & Modelling Elaboration

📚 Teacher Demonstration

Look at the picture: a person is leaning on a wall. Think about these questions:

"If the person is pushing the wall, why doesn't the wall move?"

"Why doesn't the person fall through the wall?"

Force Pairs on a Person Leaning Against a Wall

Label the force pairs — use the diagram above to help you:

Horizontal pair:

Action: Person's hand pushes the to the

Reaction: The pushes the person's hand to the

Vertical pair:

Action: Person's feet push the

Reaction: The pushes the person's feet

Now draw this in your book!

Draw a stickman leaning on a wall. Add arrows for both pairs. Use red for action and blue for reaction.

In your book, draw a person leaning on a wall. Show and label:

✅ The horizontal action-reaction pair (hand ↔ wall)

✅ The vertical action-reaction pair (feet ↔ floor)

✅ Arrows must be equal length and opposite direction

✅ Label which object each force acts on

Describe the two force pairs in full sentences:

Draw the diagram with ALL THREE pairs, including the gravity pair:

✅ Horizontal pair: Hand ↔ Wall

✅ Vertical pair: Feet ↔ Floor

✅ Gravity pair: Earth pulls person down ↔ Person pulls Earth up

Describe ALL THREE pairs in detail. Explain why the third pair is particularly hard for people to believe:

📝 Peer Assessment Criteria (Green Pen)

Check your partner's diagram:

☐ Are the arrows the same size (equal forces)?

☐ Are they in opposite directions?

☐ Are the forces acting on different objects?

☐ Are all arrows labelled clearly?

Progress Check

GTT: Consolidation Assessment

Learning Objectives Check

I can recall and identify different types of forces I can state Newton's 3rd Law and identify action-reaction force pairs I can distinguish between balanced forces and Newton's 3rd Law pairs

Foundation:

1. C — Every action has an equal and opposite reaction

2. C — Pushes back with an equal force

3. B — Different objects

Fill in: equal, opposite, different

Core:

1. Every action has an equal and opposite reaction.

2. Forces are balanced and in opposite directions — no resultant force.

3. Action-reaction pairs act on different objects; balanced forces act on the same object.

4. Person pushes floor down (action). Floor pushes person up (reaction). Equal forces, opposite directions, different objects.

5. Rocket pushes gases downward (1). Gases push rocket upward (1). Equal and opposite forces on different objects (1).

Challenge:

1. The student is wrong. Action-reaction forces DO NOT cancel out because they act on DIFFERENT objects. For something to move, we look at the resultant force on ONE object. E.g., when a rocket launches, the exhaust gas pushes the rocket up while the rocket pushes gas down — these act on different things. The rocket accelerates because the thrust on the rocket is greater than its weight.

2. The tyres push the road backwards (action). The road pushes the tyres forwards (reaction) — this is friction. These act on different objects (tyres and road). The forward friction force on the car is greater than air resistance, giving a resultant forward force. By F = ma, this causes the car to accelerate.

Self-Assessment

Skill	Confidence (1-5)
State Newton's Third Law
Identify action-reaction force pairs
Distinguish balanced forces from 3rd Law pairs
Draw and label force pair diagrams

📝 Homework

Observational Task: Find three examples of Newton's Third Law in your home (e.g., sitting on a chair, a picture hanging on a nail, walking on a rug). For each, name the action force, the reaction force, and the two objects involved.

Do Now: Anagram Challenge

Why This Matters

Recap: Newton's First & Second Laws

Think (1 min)

Pair (2 mins)

Share

Complete Newton's Laws using the word bank:

Word Bank

Newton's First Law:

Newton's Second Law:

Write out both laws from memory, then answer:

Apply: A 1500 kg car accelerates at 2 m/s². Calculate the resultant force.

Recall and extend:

2. A 60 kg skydiver falls with weight 600 N and air resistance 400 N. Calculate the resultant force and acceleration.

3. How do the First and Second Laws link together? Explain what happens when resultant force is zero vs non-zero.

Newton's Third Law

📚 Newton's Third Law of Motion

Three Key Rules

The Dog and Rope Model

🇦🇪 UAE Connection: The Hope Mars Mission

Use the keywords below to explain Newton's Third Law:

Keywords

Explain Newton's Third Law in your own words:

Give one real-world example of an action-reaction pair:

Explain how Newton's Third Law enables rocket propulsion:

Why does the rocket accelerate upwards even though the action and reaction forces are equal?

Balanced Forces vs Action-Reaction Pairs

📚 This Is the Key Distinction

⚠️ Common Misconception

Sort each example: Balanced Forces or Action-Reaction Pair?

Remember

For each example, state whether it is balanced forces or an action-reaction pair. Explain your reasoning.

a) A book resting on a table — weight acting down, reaction force acting up:

b) You push a shopping trolley forward / The trolley pushes back on your hands:

c) A fish swimming at constant speed — forward force and drag are equal:

d) The Moon orbiting Earth — Earth pulls Moon / Moon pulls Earth:

Evaluate these student statements:

Student A says: "A book on a table doesn't move because the action and reaction forces cancel out."

Student B says: "If action and reaction forces are equal and opposite, nothing should ever move."

Action-Reaction Scenarios

Remember the Rule

State the reaction force for each action:

Sentence Frame

1. 📚 A student picks up a book (exerts an upward force on the book).

2. 🌍 The Earth exerts a gravitational force on the Moon.

3. 🐒 A monkey hangs from a branch (exerts a downward force on the branch).

4. 🐎 A horse pushes the ground backwards as it gallops.

For each scenario, write the full action-reaction pair. Name both objects and both force directions.

1. A student picks up a book:

2. The Earth exerts a gravitational force on the Moon:

3. A monkey hangs from a branch:

4. A horse gallops along the ground:

5. A swimmer pushes water backwards with their hands:

Extended contexts — explain the action-reaction pairs AND link to motion:

1. A rocket launches from Earth. Explain, using Newton's Third Law, how this occurs. (3 marks)

2. A runner sprints along a track. Explain, using Newton's Third Law, how the runner moves forward. (3 marks)

3. The Moon orbits the Earth. Explain the 3rd Law pair and why the Moon moves more than the Earth. (4 marks)

4. Why do astronauts push gently when moving inside a spacecraft? (2 marks)

The Leaning Wall Task

📚 Teacher Demonstration

Force Pairs on a Person Leaning Against a Wall

Label the force pairs — use the diagram above to help you:

Horizontal pair:

Vertical pair:

Now draw this in your book!

In your book, draw a person leaning on a wall. Show and label:

Draw the diagram with ALL THREE pairs, including the gravity pair:

📝 Peer Assessment Criteria (Green Pen)

Progress Check

Learning Objectives Check

Section A — Multiple Choice (AO1)

1. Newton's Third Law states:

2. If you push a wall, the wall:

3. Action-reaction forces act on:

Section B — Fill in the Blanks

Section C — Summarise

Summarise Newton's Third Law in ONE sentence. You must include the phrase "different objects".

Section A — Short Answer (AO2)

1. Explain Newton's Third Law in a sentence. (1 mark)

2. What does it mean if forces are in equilibrium? (1 mark)