Forces
This lesson builds newton's laws and f = m a for GCSE Physics.
Use the core lesson first, then match the exam-board guidance to your school route. Many pupils meet this content through Combined Science as well as Separate Physics.
What you will learn
Exam-board fit
Exact paper labels and specification-point numbering vary by board and cohort, so match this lesson to your school route before using past-paper questions.
Force scenarios supplied on this page
Use the trolley, car and skater examples to practise resultant force, acceleration and force-pair language.
Clear explanation
Newton's first law says an object remains at rest or moves at steady velocity unless a resultant force acts.
Newton's second law links resultant force, mass and acceleration: force = mass x acceleration.
Newton's third law describes force pairs: when one object exerts a force on another, the second object exerts an equal and opposite force on the first object.
Key diagram
Worked examples
Calculating resultant force
A 1200 kg car accelerates at 2 m/s2.
force = mass x acceleration
force = 1200 x 2 = 2400
Quick checks
Choose an answer, then check your thinking.
1. A box moves at steady velocity. What is the resultant force?
2. A 5 kg object accelerates at 3 m/s2. What is the resultant force?
Practice questions
Question 1
Calculate the force needed to accelerate 8 kg at 2.5 m/s2.
Reveal answer and marking guidance
Answer: 20 N.
Marking: Credit F = m a and 8 x 2.5 = 20 N.
Question 2
A 60 N resultant force acts on a 12 kg object. Calculate acceleration.
Reveal answer and marking guidance
Answer: 5 m/s2.
Marking: Credit a = F ÷ m and 60 ÷ 12 = 5 m/s2.
Question 3
Explain why a cyclist can move at steady speed even while pedalling.
Reveal answer and marking guidance
Answer: The forward driving force balances resistive forces, so resultant force is zero.
Marking: Credit balanced forces and steady velocity.
Question 4
State the force pair when a foot pushes backwards on the ground.
Reveal answer and marking guidance
Answer: The ground pushes forwards on the foot with an equal and opposite force.
Marking: Credit forces on different objects.
Exam practice ladder
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
- Saying steady motion needs a forward resultant force.
- Using weight instead of mass in F = m a without care.
- Putting action-reaction forces on the same object.
- Forgetting acceleration units.
Exam-board guidance
All supported routes assess the core physics idea, but they may group topics, practicals and paper wording differently.
AQA GCSE Physics
AQA GCSE Physics: use this lesson for newton's laws and f = m a, then check whether your class is taking Separate Physics or Combined Science.
OCR GCSE Physics
OCR GCSE Physics: the core physics idea is shared, but Gateway and Twenty First Century may organise questions differently.
Pearson Edexcel GCSE Physics
Pearson Edexcel GCSE Physics: practise the concept, the equation use and the practical language because questions often connect them.
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: check whether your class is using the current GCSE Physics route or a newer science route, then use this lesson for the shared physics idea.
CCEA GCSE Physics
CCEA GCSE Physics: connect the idea to your unit and remember that practical skills are assessed directly.
Extension challenge
Draw a free-body diagram for a car accelerating, cruising and braking, then label the resultant force each time.
Reveal answer
Example answer: A strong extension response names the physics model, uses accurate units and explains why the evidence supports the conclusion.
Next lesson
Next, continue with Stopping Distances and Momentum.