Forces
Lesson overview
This lesson introduces the core physics idea, the useful equipment and the calculation or data skills used on this page.
What you will learn
Turning-force examples supplied on this page
Use the door handle, seesaw, spanner and bicycle gear examples to practise moments reasoning.
Moments, levers and gears infographic
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.
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.
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.
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 moments, equilibrium, levers and gears.
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 Hooke's Law and Elastic Energy.