H2 Physics Moments and Equilibrium Practical: Pivot, Torque and Centre of Mass
01 May 2026, 00:00 Z
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Q: What is the key skill in a H2 Physics moments practical?
A: It is balancing forces and distances about a pivot, while accounting for the metre rule's own weight, distance uncertainty, and pivot friction.
TL;DR
In a moments practical, balance a metre rule on a pivot, record forces and perpendicular distances, then test whether clockwise moment equals anticlockwise moment. The formula is simple. The scoring detail is in finding the rule's centre of gravity, measuring every distance from the pivot, and explaining residual imbalance using quantified errors.
Use this with H2 Physics practical lab mastery, H2 Physics Paper 4 spreadsheet skills, and H2 Physics ACE evaluation.
Status: SEAB H2 Physics 9478 syllabus checked 2026-05-01. Forces and Moments is in the syllabus, and the Paper 4 apparatus list includes pivot, pulley, Newton meters, masses, rules, and stands. This page prepares the technique family; it does not predict a specific Paper 4 setup.
1 | Theory In One Minute
The moment of a force about a pivot is:
moment = force x perpendicular distance from pivot
For equilibrium:
- Resultant force is zero.
- Resultant moment is zero.
- Sum of clockwise moments equals sum of anticlockwise moments.
If the metre rule is not pivoted exactly at its centre of gravity, the rule's own weight creates a moment and must be included.
2 | Basic Setup
Typical apparatus:
- Metre rule
- Pivot or knife edge
- Mass hangers and slotted masses
- Retort stand and clamp
- Newton meter if the force is applied by pull rather than by mass
- Set square or vertical reference if needed
Before adding loads, find the balance point of the rule alone. This is the rule's centre of gravity. Do not assume it is exactly at the 50.0 cm mark.
3 | Method: Unknown Mass Example
- Balance the rule alone and record its centre of gravity.
- Place the pivot at a chosen mark.
- Hang a known mass on one side.
- Hang the unknown mass on the other side.
- Adjust position until the rule is horizontal.
