This topic summary covers Knowledge Organiser: Moments and Levers within Moments & Levers for GCSE Physics. Revise Moments & Levers in Forces for GCSE Physics with 13 exam-style questions and 10 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 14 of 14 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Knowledge Organiser: Moments and Levers
Key Terms
- Moment: Turning effect of a force (Nm)
- Pivot/fulcrum: Fixed rotation point
- Equilibrium: Zero resultant force and moment
- Lever: Simple machine using pivot to multiply force
Key Facts
- Larger distance from pivot = larger moment
- Principle of moments: CW moments = ACW moments (in balance)
- Levers trade force for distance (energy conserved)
- Weight acts through centre of mass
Key Equations
- M = F × d (perpendicular distance)
- For balance: Sum CW = Sum ACW
- Units: Moment in Nm, force in N, distance in m
Exam Tips
- Always use perpendicular distance
- Use W = mg to find weights first
- State "principle of moments" in 3+ mark questions
- Centre of mass for uniform object = geometric centre
Common Mistakes
- Using slant distance instead of perpendicular distance: The distance in M = F × d must be the perpendicular distance from the pivot to the line of action of the force — not the length of the lever arm
- Forgetting to convert weight: Convert mass to weight (W = m × g) before using in moment calculations — do not use kg values in the moment equation
- Not stating the principle of moments: For 3+ mark balance questions, always state "sum of clockwise moments = sum of anticlockwise moments about the pivot"
- Confusing moment and force: A larger force does not always produce a larger moment — a small force at a large distance can produce a bigger moment than a large force close to the pivot
- Placing centre of mass wrongly for irregular shapes: Centre of mass is found by suspension method (hanging from different points) — it is not always at the geometric centre for irregular objects
Practice questions for Moments & Levers
What is a moment?
State the principle of moments.
Quick recall flashcards
Key Concepts
Unit: Newton metres (Nm)
Key Concepts
A moment is the turning effect of a force