Free GCSE Physics lesson: Forces and Motion
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Free Lessons -> GCSE / Key Stage 4 -> Physics -> Forces and Motion

Lesson 3 · GCSE / Key Stage 4 · Physics

Forces and motion basics

Learn how resultant force, speed, acceleration and motion graphs work together in GCSE Physics.

Qualification: GCSE Subject: Physics Forces

Forces

Lesson overview

This lesson introduces the core physics idea, the useful equipment and the calculation or data skills used on this page.

FocusForces, speed and acceleration
Time45-60 minutes
EquipmentCalculator, ruler and graph paper if practising graphs.
Practical linkNo separate practical method focus
Maths tagsM1 substitution with units, M6 ratio and percentage

What you will learn

  • Distinguish balanced and unbalanced forces.
  • Calculate speed from distance and time.
  • Explain acceleration as a change in velocity over time.
  • Read simple distance-time and velocity-time graph features.

Motion data supplied on this page

Use the runner and trolley examples below to practise calculating speed, identifying resultant force and explaining acceleration.

Forces and motion infographic

Infographic explaining GCSE Physics forces and motion, including resultant force, acceleration, motion graphs and everyday force examples.
Use this visual to connect forces, motion changes and graph evidence.Download visual

Clear explanation

A force is a push or pull. When forces are balanced, the resultant force is zero. An object can stay still or keep moving at steady velocity.

When the resultant force is not zero, the object accelerates. That means its velocity changes: it may speed up, slow down or change direction.

Speed links distance and time. Acceleration links change in velocity and time. Graphs show the same ideas visually.

Key graph

Distance-time graph with moving and stationary sections A distance-time graph rises from zero to forty metres in eight seconds, then becomes horizontal from eight to twelve seconds to show the object is stationary. time / s distance / m moving stationary
Graph: the sloping section shows movement and the horizontal section shows no change in distance.

Worked examples

Runner speed

A runner travels 100 m in 12.5 s.

speed = distance ÷ time

speed = 100 ÷ 12.5 = 8

Answer: The runner's speed is 8 m/s.

Quick checks

Choose an answer, then check your thinking.

1. A car travels at steady velocity in a straight line. What is the resultant force?

2. A trolley changes from 2 m/s to 10 m/s in 4 s. What is its acceleration?

Practice questions

Question 1

A cyclist travels 150 m in 30 s. Calculate the average speed.

Reveal answer and marking guidance

Answer: 5 m/s.

Marking: Credit speed = distance ÷ time and 150 ÷ 30 = 5 m/s.

Question 2

A box has 12 N pushing right and 7 N friction left. What is the resultant force?

Reveal answer and marking guidance

Answer: 5 N to the right.

Marking: Credit subtracting opposing forces and keeping the direction.

Question 3

A toy car slows from 9 m/s to 3 m/s in 2 s. Calculate the acceleration.

Reveal answer and marking guidance

Answer: -3 m/s², or 3 m/s² deceleration.

Marking: Credit change in velocity = 3 - 9 = -6 m/s, then -6 ÷ 2 = -3 m/s².

Question 4

On a distance-time graph, what does a horizontal line show?

Reveal answer and marking guidance

Answer: The object is stationary.

Marking: Credit no change in distance as time passes.

Practice ladder

FluencyRecall the key definition, unit, equation or model before using the lesson questions.
ApplicationApply forces, speed and acceleration to an unfamiliar device, practical setup or data description.
Practical interpretationUse evidence, graph features, uncertainty, method quality or conclusion wording where the question asks you to evaluate.
Maths skillM1 substitution with units

Answers and marking guidance

The exact practice answers are hidden under each question so you can try first. For this lesson, marks come from using the correct physics model, choosing the right equation where needed, keeping units with values, and explaining changes with precise words such as transfer, resultant force, acceleration, evidence and uncertainty.

Common mistakes

  • Confusing speed with acceleration.
  • Forgetting direction when finding a resultant force.
  • Saying a moving object must have a forward resultant force even when it moves steadily.
  • Using total velocity instead of change in velocity for acceleration.

Extension challenge

Sketch a velocity-time graph for an object that accelerates, moves steadily, then decelerates. Label where the resultant force is non-zero.

Reveal answer

Example answer: A strong extension response names the physics model, uses accurate units and explains why the evidence supports the conclusion.

Exam-board guidance

Short board notes only. Learn the core physics above first.

AQA GCSE Physics

AQA GCSE Physics: often rewards clear physics explanations, correct equations, units and practical evidence for forces, speed and acceleration.

OCR GCSE Physics

OCR GCSE Physics: often values precise definitions, clear working, graph interpretation and links between models and evidence.

Pearson Edexcel GCSE Physics

Pearson Edexcel GCSE Physics: often combines the concept with equation use, data handling and practical interpretation.

Eduqas GCSE Physics

Eduqas GCSE Physics: learn the core explanation and practise applying it to unfamiliar contexts, data and practical questions.

WJEC Wales

WJEC Wales: often expects accurate terms, units and evidence-based explanations using the shared physics idea.

CCEA GCSE Physics

CCEA GCSE Physics: connect the idea to your current unit and use the same practical method language your class uses.

Next lesson

Next, continue with Electricity, Charge and Circuits.

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