Forces - Year 9 Physics

Do Now: Activating Prior Knowledge

GTT: Activating Hard Thinking Retrieval Practice

Why This Matters

Retrieving what you already know about forces strengthens your memory and prepares your brain for new learning. This is called retrieval practice - one of the most powerful learning strategies.

Imagine a busy scene:

A car driving on a road, a plane flying overhead, a person swimming, and a book resting on a table.

Think about ALL the forces acting on each object!

Task: List forces using the word bank

Word Bank

weightfrictionair resistancethrustupthrusttensionreaction forcedrag

Sentence starter: "One force I can see is _______ which acts on the _______ because..."

Write at least 4 forces you can identify:

Task: Identify and explain forces

List as many forces as you can. For each: name the force, state which object it acts on, describe the direction.

Your response (aim for at least 6 forces):

Task: Analyse force pairs and equilibrium

1. List all forces (aim for 8+):

2. Which forces are balanced? What does this tell us about motion?

3. Pick one object - what would happen if one force was removed?

Example Forces:

Car: Weight, reaction force, thrust, friction, air resistance
Plane: Weight, lift, thrust, drag
Swimmer: Weight, upthrust, forward force, drag
Book: Weight, reaction force

Recall: What Do You Remember About Forces?

GTT: Structuring Spaced Retrieval

🤔

Think (2 mins)

Silently write down 5 things you remember about forces.

👥

Pair (2 mins)

Compare your list with a partner. Add any ideas they have.

Complete these statements:

1. A force is a _______ or a _______

2. Forces are measured in _______ (N)

3. We use a _______ _______ to measure forces

4. When forces are _______, objects stay still or move at constant speed

Write 5 facts about forces

Fact 1:

Fact 2:

Fact 3:

Fact 4:

Fact 5:

Create a concept map about forces

Key Concepts to Connect

Forces • Newton • Push • Pull • Balanced • Unbalanced • Acceleration • Speed • Direction • Contact • Non-contact

Write at least 5 connections:

Vectors and Scalars

GTT: Understanding Content Dual Coding

Key Definitions

Vector quantity: Has both SIZE (magnitude) and DIRECTION

Scalar quantity: Has only SIZE (magnitude)

Forces are vector quantities - we need to know how big AND which direction!

50 N →

VECTOR: 50N to the right

5 kg

SCALAR: 5kg (no direction)

Sort these quantities

Remember

Ask: "Does this quantity have a direction?" YES = Vector. NO = Scalar.

Quantity	Vector or Scalar?
Speed (30 mph)
Velocity (30 mph North)
Force (50N upwards)
Mass (10 kg)

Explain and Apply

1. Explain why force is a vector quantity:

2. A car: forward force 5000N, friction 3000N. What is the resultant?

Resultant: N, Direction:

Analyse and Create

1. "My weight is 500N" - is this correct? Explain:

2. Why is direction important when designing bridges?

Name That Force!

GTT: Maximising Opportunity Concrete Examples

Contact vs Non-Contact Forces

Contact forces: Objects must touch (friction, tension, air resistance, reaction force)

Non-contact forces: Act at a distance (gravity, magnetic force, electrostatic force)

🚗 Moving Car - Select all forces that apply:

Weight Reaction force Thrust Friction Air resistance Upthrust

Force Reminder

Weight: Always DOWNWARDS
Reaction: PERPENDICULAR to surface
Friction: OPPOSITE to motion

Identify and describe forces for each scenario:

🤸 Gymnast on Rings

Forces acting:

🏊 Diver Swimming

Forces acting:

Complete Force Analysis

Skydiver at constant speed:

List all forces and explain why they're not accelerating:

Drawing Force Diagrams

GTT: Creating Supportive Environment Elaboration

Force Diagram Rules

Draw arrows FROM the object in direction force acts
Arrow LENGTH shows force SIZE
Label each arrow with force name

Step-by-Step Guide

Identify the object
Draw weight arrow DOWN
If touching surface, draw reaction UP
If moving, add friction opposite to motion

List forces for a falling apple:

Draw diagrams for:

Rock Climber hanging from rope

List forces and state if balanced:

Box on a 30° slope - analyse the forces:

Why doesn't weight act straight down the slope?

Practical: Investigating Friction

GTT: Activating Hard Thinking Active Learning

Aim

To investigate which material has the greatest friction.

Equipment

Newton meter
Wooden block
Different surface materials

Results Table

Material	Test 1 (N)	Test 2 (N)	Test 3 (N)	Average
Sandpaper
Cardboard
Plastic

Conclusion: "The material with greatest friction was _______ because it needed _______ N to move."

Prediction - which material will have most friction? Why?

Analysis - What is the relationship between surface roughness and friction?

Design an extension: What other variable could you test?

How are friction investigations used in designing car tyres?

Do Now: Forces Acting on You

GTT: Activating Hard Thinking Retrieval Practice

Think About This...

Right now, as you sit in your seat, multiple forces are acting on your body. Can you identify them all?

🧑‍🎓

How many forces are acting on YOU right now?

Think about: What's pulling you down? What's stopping you falling through your chair?

Use the word bank to identify forces acting on you:

Word Bank

weightreaction forcefrictionair resistancetension

Forces acting on me right now:

List and explain each force:

For each force, state: name, direction, and what causes it:

Analyse the force situation:

1. List all forces with approximate sizes (use N):

2. Are these forces balanced? How do you know?

3. What would happen if the chair suddenly disappeared?

Representing Forces

Teacher-Led GTT: Understanding Content Dual Coding

📚 Teacher Explanation

We represent forces by drawing arrows. The arrow tells us two important things:

→→→→→

Big Force

→→

Small Force

Arrow LENGTH = SIZE of force | Arrow DIRECTION = Direction force acts

🚀 Worked Example: Rocket

The thrust arrow is longer because thrust > weight (rocket accelerates upward)

Copy these key points into your book:

1. Forces are represented by arrows

2. The length of the arrow shows the size of the force

3. The direction of the arrow shows which way the force acts

In your book, draw and label a rocket showing thrust and weight:

Draw force diagrams for:

1. A car accelerating (thrust > friction):

2. A plane flying at constant speed (thrust = drag):

Compare these situations:

How would the force arrows differ for a rocket at launch vs a rocket at constant speed?

Calculating Resultant Forces

Teacher Modelling GTT: Structuring Worked Examples

📚 Key Rules for Resultant Force

Same Direction?

→ + → = →→

ADD them together

Opposite Directions?

→ ← = ?

SUBTRACT smaller from larger

🎯 Worked Example 1: Same Direction

Situation: Two people push a car. Person A pushes with 200N, Person B pushes with 150N. Both push RIGHT.

Method: Same direction → ADD

Calculation: 200N + 150N = 350N to the right

🎯 Worked Example 2: Opposite Directions

Situation: A car has thrust of 5000N forwards and friction of 3000N backwards.

Method: Opposite directions → SUBTRACT

Calculation: 5000N - 3000N = 2000N forwards

Result: Car accelerates forwards

🔑 Balanced Forces (Resultant = 0)

If forces are equal and opposite, the resultant force is 0N.

This means the object is either: Stationary OR Moving at constant speed

We say the forces are BALANCED.

Your Turn - Follow the steps:

1. Hot Air Balloon: Weight = 6N down, Upthrust = 10N up

Step-by-step

a) Are forces same or opposite direction?

b) So we should (add/subtract)?

c) Calculation: ___N - ___N = N

d) Direction of resultant:

2. Fish Swimming: Forward force = 0.5N, Drag = 0.5N

Resultant = N

The fish will (accelerate/move at constant speed/stop):

Calculate the resultant force:

Situation	Forces	Resultant	Effect
Book on table	Weight 10N down, Reaction 10N up
Apple falling	Weight 1N down, Air resistance 0.5N up
Car braking	Thrust 2000N, Friction 5000N opposite

Multi-directional problems:

Helicopter: Thrust = 500N forward, Drag = 1000N backward, Lift = 12000N up, Weight = 15000N down

a) Horizontal resultant:

b) Vertical resultant:

c) Describe what happens to the helicopter:

Newton's First Law

Teacher-Led GTT: Understanding Content Elaboration

📚 Newton's First Law of Motion

"A moving object will continue to move at the same speed and direction unless an external force acts on it.

Likewise, a stationary object will remain at rest unless an external force acts on it."

What This Means:

If forces are...	Then velocity...
BALANCED (resultant = 0)	Will NOT change (stays still or constant speed)
UNBALANCED (resultant ≠ 0)	WILL change (speeds up, slows down, or changes direction)

Complete Newton's First Law using the word bank:

Word Bank

movingspeedforceobjectrestexternal

A object will continue to move at the same and direction unless an external acts on it.

Likewise, a stationary will remain at unless an force acts on it.

In your book, draw diagrams showing:

Balanced Forces: A coffee cup at rest on a table

Describe your diagram and explain why it doesn't move:

Unbalanced Forces: A car accelerating from traffic lights

Describe your diagram and explain what happens:

Apply Newton's First Law:

A passenger in a car lurches forward when the car brakes suddenly. Use Newton's First Law to explain why:

Why do objects in space keep moving forever (if no forces act)?

Practice Problems

GTT: Activating Hard Thinking Deliberate Practice

⏱️ Timed Practice - 10 minutes

Calculate the resultant force for each situation. Show your working!

Calculate with support:

1. 🎈 Hot Air Balloon

Upthrust: 10N ↑ Weight: 6N ↓

Opposite directions, so SUBTRACT: 10 - 6 = ?

Resultant = N

2. 🐟 Fish

Forward: 4N → Drag: 0.5N ←

Resultant = N

3. 📚 Book

Weight: 30N ↓ Reaction: 30N ↑

Resultant = N (What happens to the book? )

Calculate the resultant:

1. Hot Air Balloon: Weight 6N, Upthrust 10N

Resultant = Direction:

2. Fish: Forward 4N, Drag 0.5N

Resultant = Direction:

3. Book: Weight 30N, Reaction 30N

Resultant = The book is:

4. Paper ball: Weight 24N, Air resistance 20N, Throw force 10N up

Resultant = Direction:

5. Apple: Weight 11N, Air resistance 10N up, Wind 4N right

Vertical resultant =

Horizontal resultant =

Extension problems:

🚗 Car on slope: Weight component down slope = 3N, Friction up slope = 1N, Engine force = ?

The car moves at constant speed up the slope. What is the engine force?

🔺 Triangle Problem: Forces of 3N right and 4N up act on an object.

Using Pythagoras, calculate the resultant force:

Show working:

Resultant = N

Answers:

1. Balloon: 4N upwards
2. Fish: 3.5N forwards
3. Book: 0N (balanced - stationary)
4. Paper ball: 34N downwards (24 + 20 - 10)
5. Apple: 1N down, 4N right
Extension Triangle: 5N (3² + 4² = 25, √25 = 5)

Progress Check

GTT: Consolidation Assessment

Learning Objectives Check

I can identify forces in a given situation I can calculate the resultant force acting on an object I can recall Newton's first law

Q1: Match the force diagram to what happens:

Diagram Description	What Happens?
Big arrow RIGHT, small arrow LEFT
Big arrow LEFT, small arrow RIGHT
Equal arrows opposite directions

Q2: A book has forces of 11N right and 7N left.

a) Which way will it move?

b) What is the resultant force?

Q3: Helicopter Problem

A helicopter has: Lift = 18000N up, Weight = 15000N down, Thrust = 1200N forward, Drag = 1200N backward, Velocity = 100 m/s forward

a) What is the resultant force horizontally? N

b) What will happen to the speed horizontally?

c) What is the resultant force vertically? N ()

d) What will happen to the helicopter vertically?

Q4: Extended Analysis

The pilot adjusts controls: Forward force = 500N, Drag = 1000N, Lift = 12000N, Weight = 15000N

a) Resultant horizontally: N to the

b) Resultant vertically: N ()

c) Describe what will happen to the helicopter's velocity:

Q5: Explain using Newton's First Law

Why does a spacecraft in deep space keep moving at constant velocity without using its engines?

Progress Check Answers:

Q1: Accelerates forward | Slows down | Constant speed
Q2: a) Right, b) 4N
Q3: a) 0N, b) Constant speed, c) 3000N upwards, d) Accelerates upward
Q4: a) 500N backwards, b) 3000N downwards, c) Slows down and descends
Q5: No external forces act on it, so by Newton's First Law it continues at constant velocity

Self-Assessment

Skill	Confidence (1-5)
Calculate resultant of forces in same direction
Calculate resultant of forces in opposite directions
Explain what balanced forces mean
State Newton's First Law

Do Now: Linking Force and Motion

GTT: Activating Hard Thinking Retrieval Practice

Recall from Last Lesson

We learned about resultant forces and Newton's First Law. Today we'll explore what happens when forces are UNBALANCED.

🚗 ➡️ 💨

What happens when you press the accelerator in a car?

Think about: What changes? What forces are involved?

Complete these recall questions:

1. When forces are balanced, an object will stay _______ or move at _______ speed.

2. When forces are unbalanced, the object will _______ (speed up or slow down).

3. The change in speed is called _______.

Link these concepts:

1. A car accelerates from traffic lights. Describe the forces and what's happening:

2. What's the connection between resultant force and acceleration?

Predict and explain:

1. Two identical cars have different engines. Car A has a 200 HP engine, Car B has a 100 HP engine. Which will accelerate faster from rest? Explain using forces:

2. If you doubled the resultant force on an object, what do you think would happen to its acceleration?

The Effect of Resultant Force

Teacher-Led GTT: Understanding Content Dual Coding

📚 Key Concept: Force Causes Acceleration

When a resultant force acts on an object, it ACCELERATES

⬆️ Force

Bigger resultant force

= Greater acceleration

⬆️ Mass

Bigger mass (heavier object)

= Smaller acceleration

🔑 Remember:

Acceleration = how quickly velocity changes
Acceleration can mean speeding UP or slowing DOWN (deceleration)
The direction of acceleration is the same as the resultant force

🎯 Real World Example: Pushing a Shopping Trolley

Empty trolley:

Small mass → Easy to accelerate → Speeds up quickly

Full trolley:

Large mass → Harder to accelerate → Speeds up slowly

Copy these key points into your book:

1. A resultant force causes an object to accelerate

2. Bigger force = greater acceleration

3. Bigger mass = smaller acceleration

4. Acceleration is measured in m/s² (metres per second squared)

Quick Check: Which accelerates more easily?

A bicycle or a truck (with the same push force)?

Why?

Apply your understanding:

Compare these situations:

Situation	Acceleration (high/medium/low)	Reason
Sports car (small mass, big engine)
Lorry (big mass, big engine)
Bicycle (small mass, small force)

Analyse and explain:

1. A rocket burns fuel as it travels. How does this affect its acceleration over time? (Hint: what happens to its mass?)

2. Explain why race cars are made as light as possible:

The Acceleration Formula

Teacher Modelling GTT: Structuring Worked Examples

📚 The Formula

acceleration = change in velocity

time

a = (v - u) / t

a = acceleration (m/s²)

v = final velocity (m/s)

u = initial velocity (m/s) — sometimes called starting velocity

t = time taken (s)

🎯 Worked Example 1

Question: A car accelerates from 10 m/s to 30 m/s in 5 seconds. Calculate its acceleration.

Step 1 - Write what you know: u = 10 m/s, v = 30 m/s, t = 5 s

Step 2 - Write the formula: a = (v - u) / t

Step 3 - Substitute: a = (30 - 10) / 5

Step 4 - Calculate: a = 20 / 5 = 4 m/s²

🎯 Worked Example 2 (Deceleration)

Question: A bike slows from 15 m/s to 5 m/s in 2 seconds. Calculate its acceleration.

Step 1: u = 15 m/s, v = 5 m/s, t = 2 s

Step 2: a = (v - u) / t

Step 3: a = (5 - 15) / 2

Step 4: a = -10 / 2 = -5 m/s²

Note: Negative acceleration means slowing down (deceleration)

Follow the steps to calculate acceleration:

Q1: A sprinter accelerates from 0 m/s to 12 m/s in 4 seconds.

Step-by-step scaffold:

Step 1 - What do you know?

u (starting velocity) = m/s

v (final velocity) = m/s

t (time) = s

Step 2 - Write the formula: a = (v - u) / t

Step 3 - Substitute numbers:

a = ( - ) /

Step 4 - Calculate:

a = m/s²

Q2: A train slows from 20 m/s to 0 m/s in 10 seconds.

u = m/s, v = m/s, t = s

a = ( - ) / = m/s²

Calculate acceleration (show working):

Q1: A car goes from 5 m/s to 25 m/s in 8 seconds.

Q2: A cyclist slows from 18 m/s to 6 m/s in 3 seconds.

Q3: A rocket accelerates from rest to 100 m/s in 20 seconds.

Extended calculations:

Q1: Rearranging - A car has acceleration 3 m/s². It starts at 10 m/s. How fast is it going after 6 seconds?

Q2: A plane needs to reach 80 m/s to take off. If it accelerates at 4 m/s² from rest, how long does this take?

Record the time taken for the trolley to travel a set distance
Set up the track with trolley, string, pulley and weights
Calculate acceleration using a = (v-u)/t
Release the trolley and start timing
Repeat 3 times and calculate average
Add more weights and repeat

Data Analysis: Using Practice Data

GTT: Maximising Opportunity Deliberate Practice

📊 Practice Data from the Investigation

Here are results from an experiment where force was changed and acceleration was measured.

📚 Experiment Results

Force (N)	Final velocity v (m/s)	Time t (s)	Acceleration a (m/s²)
1.0	0.5	2.5	?
2.0	1.0	2.5	?
3.0	1.5	2.5	?
4.0	2.0	2.5	?
5.0	2.5	2.5	?

Calculate the acceleration for each row:

Row 1: Force = 1.0 N

u = 0 m/s, v = 0.5 m/s, t = 2.5 s

a = (v - u) / t

a = (0.5 - 0) / 2.5

a = 0.5 / 2.5 = m/s²

Row 2: Force = 2.0 N

u = m/s, v = m/s, t = s

a = ( - ) /

a = m/s²

Row 3: Force = 3.0 N

a = m/s²

Conclusion starter: "As the force increased, the acceleration _______. This shows that force and acceleration are _______ related."

Complete the calculations and analysis:

Calculate acceleration for all 5 rows:

Force (N)	Your calculation	Acceleration (m/s²)
1.0
2.0
3.0
4.0
5.0

Describe the pattern in your results:

If you plotted Force (x-axis) against Acceleration (y-axis), what would the graph look like?

Full data analysis:

1. Calculate all accelerations and complete this table:

Force (N)	Acceleration (m/s²)	Force ÷ Acceleration
1.0
2.0
3.0
4.0
5.0

2. What do you notice about the Force ÷ Acceleration column? What does this value represent?

3. Use F = ma to calculate the mass of the trolley from your data:

4. Evaluate the investigation - what are possible sources of error?

5. How could the accuracy of this investigation be improved?

Calculated Accelerations:

1.0 N → a = 0.2 m/s²
2.0 N → a = 0.4 m/s²
3.0 N → a = 0.6 m/s²
4.0 N → a = 0.8 m/s²
5.0 N → a = 1.0 m/s²

Pattern: Force ÷ Acceleration = 5 kg (this is the mass of the trolley)

Relationship: Force and acceleration are directly proportional (F = ma)

Progress Check

GTT: Consolidation Assessment

Learning Objectives Check

I can describe the effect of a resultant force on an object I can design an investigation to see how force affects acceleration I can use a = (v - u) / t to calculate acceleration

Quick Quiz:

1. What does a resultant force cause an object to do?

Stay still Accelerate Change colour

2. In the formula a = (v - u) / t, what does 'u' represent?

Final velocity Initial velocity Acceleration

3. A car goes from 0 to 20 m/s in 10 seconds. What is the acceleration?

200 m/s² 2 m/s² 0.5 m/s²

4. In an investigation, the variable you change on purpose is called:

Dependent variable Independent variable Control variable

Short Answer Questions:

1. Explain why a heavier object needs more force to achieve the same acceleration as a lighter object:

2. Calculate: A runner accelerates from 2 m/s to 8 m/s in 3 seconds. Show your working:

3. Name the independent, dependent, and two control variables for investigating how force affects acceleration:

Extended Response:

1. (6 marks) A student investigated how force affects acceleration. Their results are shown:

Force (N)	Acceleration (m/s²)
2	1
4	2
6	2.5
8	4

a) Identify the anomalous result and suggest what might have caused it:

b) Calculate the mass of the trolley using the non-anomalous results:

c) Suggest two improvements to make the results more reliable:

2. A car accelerates from 15 m/s to 35 m/s in 8 seconds, then decelerates to 0 m/s in 5 seconds.

a) Calculate the acceleration during the first phase:

b) Calculate the deceleration during the second phase:

c) If the car has a mass of 1200 kg, calculate the resultant force during acceleration (use F = ma):

Answers:

Foundation Q3: 2 m/s² (20-0)/10 = 2
Core Q2: a = (8-2)/3 = 2 m/s²
Challenge Q1: Anomaly is 6N → 2.5 m/s² (should be 3). Mass = F/a = 2/1 = 2 kg
Challenge Q2: a) (35-15)/8 = 2.5 m/s², b) (0-35)/5 = -7 m/s², c) F = 1200 × 2.5 = 3000 N

Self-Assessment

Skill	Confidence (1-5)
Describe the effect of resultant force on acceleration
Use a = (v-u)/t to calculate acceleration
Identify variables in an investigation
Plan a fair test investigation

Do Now: Activating Prior Knowledge

Why This Matters

Task: List forces using the word bank

Word Bank

Task: Identify and explain forces

Task: Analyse force pairs and equilibrium

Example Forces:

Recall: What Do You Remember About Forces?

Think (2 mins)

Pair (2 mins)

Share (3 mins)

Complete these statements:

Write 5 facts about forces

Create a concept map about forces

Key Concepts to Connect

Vectors and Scalars

Key Definitions

Sort these quantities

Remember

Explain and Apply

1. Explain why force is a vector quantity:

2. A car: forward force 5000N, friction 3000N. What is the resultant?

Analyse and Create

1. "My weight is 500N" - is this correct? Explain:

2. Why is direction important when designing bridges?

Name That Force!

Contact vs Non-Contact Forces

🚗 Moving Car - Select all forces that apply:

Force Reminder

Identify and describe forces for each scenario:

🤸 Gymnast on Rings

🏊 Diver Swimming

Complete Force Analysis

Skydiver at constant speed:

Drawing Force Diagrams

Force Diagram Rules

Step-by-Step Guide

Draw diagrams for:

Rock Climber hanging from rope

Box on a 30° slope - analyse the forces:

Practical: Investigating Friction

Aim

Equipment

Results Table

Lesson 1 Review

Check Your Progress

1. What is a force?

2. Which is a vector quantity?

3. Which is a non-contact force?

Explain why a book stays on a table:

Give one example of a contact force and one non-contact force:

Describe how forces change for a skydiver from jump to landing:

Do Now: Forces Acting on You

Think About This...

Use the word bank to identify forces acting on you:

Word Bank

List and explain each force:

Analyse the force situation:

Representing Forces

📚 Teacher Explanation

🚀 Worked Example: Rocket

Copy these key points into your book:

Draw force diagrams for:

Compare these situations:

Calculating Resultant Forces

📚 Key Rules for Resultant Force

🎯 Worked Example 1: Same Direction

🎯 Worked Example 2: Opposite Directions

🔑 Balanced Forces (Resultant = 0)

Your Turn - Follow the steps:

1. Hot Air Balloon: Weight = 6N down, Upthrust = 10N up

Step-by-step

2. Fish Swimming: Forward force = 0.5N, Drag = 0.5N

Calculate the resultant force:

Multi-directional problems:

Helicopter: Thrust = 500N forward, Drag = 1000N backward, Lift = 12000N up, Weight = 15000N down

Newton's First Law

📚 Newton's First Law of Motion

What This Means:

Complete Newton's First Law using the word bank: