Moments, levers and gears: GCSE Physics
Moment of a force, equilibrium, levers and gears as force multipliers
The short version
Moment = force × perpendicular distance. In equilibrium clockwise moments equal anticlockwise. Gears trade force and rotation speed.
Key idea
Unit: Nm. d must be perpendicular to the force (or use the perpendicular component of F)
Grade 2–3: Turning is easier with a bigger push or a longer handle.
Grade 5–6: I use moment = F x d and I quote Nm.
Grade 9: I insist on perpendicular distance and I can say a force through the pivot gives zero moment.
Go a bit deeper
Same pivot for every term. Resultant force is also zero if it is not accelerating
Grade 2–3: The heavy person sits nearer the middle so the seesaw does not slam down.
Grade 5–6: I can write clockwise = anticlockwise and find one unknown.
Grade 9: I include the beam's weight at its centre of mass when it is not "light", and I check forces up = forces down as well.
Worked example
Worked example
Grade 2–3: Turning is easier with a bigger push or a longer handle. Grade 5–6: I use moment = F x d and I quote Nm. Grade 9: I insist on perpendicular distance and I can say a force through the pivot gives zero moment.
Lessons in this topic
- What a moment is
- Equilibrium of moments
- Levers
- Gears
- Centre of mass and stability
In the app each lesson is video (when we have a real YouTube id) then intro, learn and summary steps.
What the examiner wants
Calculate moments, solve see-saw equilibrium, and explain levers and gear ratios including force and distance trade-off.
Try these questions
Cover the answers and have a go first. Worked solutions are underneath.
Moment of a force =
The unit of moment is
If a force points straight at the pivot, the moment is
For a balanced see-saw
Common mistakes
- Do not use the distance along the door if the force is at an angle - it must be perpendicular. Do not write the unit as N/m (that is spring constant).
- Do not add the forces and call that a moment. Distances are from the pivot you chose, not from the end of the beam unless that is the pivot.
- Tweezers are not a force multiplier. Do not forget to say which point is the pivot.
- Do not say the large gear "creates extra force from nowhere". The force at the teeth is the same; the moment is larger because r is larger.
Answers and working
Frequently asked questions
Is GCSE Moments, levers and gears on Combined Science and Triple?
Moments, levers and gears is Triple-only Physics. Combined Science students can skip it.
Which exam board is this Moments, levers and gears page for?
The ideas are board-agnostic for AQA, Edexcel, OCR, WJEC and CCEA. Paper lengths and question numbers differ — check your specification.
Is Moments, levers and gears Foundation or Higher?
The core ideas appear on both tiers. Higher papers add extra application and some HT-only detail, marked in lessons with a Higher badge.
Learn, try, get feedback, fix the mistake
Open the stepped lesson, then the quiz with hints. Required-practical and calculation questions use the same method you will need in the paper.
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