Forces
This lesson builds moments, equilibrium, levers and gears 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.
Turning-force examples supplied on this page
Use the door handle, seesaw, spanner and bicycle gear examples to practise moments reasoning.
Clear explanation
A moment is the turning effect of a force. moment = force x perpendicular distance from the pivot.
An object is balanced when the total clockwise moment equals the total anticlockwise moment. The distance must be measured at right angles from the pivot to the line of action of the force.
Levers increase turning effect by increasing distance from the pivot. Gears transfer turning effects and can trade rotational speed for a larger turning force.
Key diagram
Worked examples
Moment of a force
A 20 N force acts 0.30 m from a pivot.
moment = force x distance
moment = 20 x 0.30
Quick checks
Choose an answer, then check your thinking.
1. Which distance is used in a moment calculation?
2. When is a seesaw balanced?
Practice questions
Question 1
Calculate the moment of a 15 N force acting 0.4 m from a pivot.
Reveal answer and marking guidance
Answer: 6 N m.
Marking: Credit 15 x 0.4 = 6 N m.
Question 2
Why is a long spanner useful for loosening a tight nut?
Reveal answer and marking guidance
Answer: It increases the distance from the pivot, increasing the moment for the same force.
Marking: Credit larger distance giving larger turning effect.
Question 3
A 10 N force acts 0.5 m to the left of a pivot. What force at 0.25 m to the right would balance it?
Reveal answer and marking guidance
Answer: 20 N.
Marking: Credit left moment 5 N m and force = 5 ÷ 0.25 = 20 N.
Question 4
What can gears change in a machine?
Reveal answer and marking guidance
Answer: They can change rotational speed, direction and turning force.
Marking: Credit any two valid gear effects.
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
- Using centimetres without converting to metres.
- Forgetting the distance must be perpendicular.
- Adding clockwise and anticlockwise moments when checking balance.
- Thinking a longer lever changes the force itself rather than the turning effect.
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 moments, equilibrium, levers and gears, 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
Design a balanced seesaw question with unequal distances and solve for the missing force.
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 Hooke's Law and Elastic Energy.