4.2.1—The principle of moments
- Syllabus
- 9702–2028–2029
- Objective
- 4.2.1
- Level
- AS
In rotational equilibrium, clockwise and anticlockwise moments about a pivot balance
The principle of moments states that if a body is in equilibrium, the sum of clockwise moments about any point equals the sum of anticlockwise moments.
Choose a convenient pivot, use perpendicular distances and take a consistent sign convention. A force through the pivot has zero moment.
A 20 N load 0.40 m from a pivot is balanced by a 10 N load at 0.80 m on the opposite side.
Moment balance alone does not guarantee translational equilibrium; the resultant force must also be zero.
ConceptA-Level CAIE Physics AS