Statics › Section D · Moments and static equivalence › Topic D.4
Moments in 3D and about an axis
In three dimensions a moment can point in any direction, and the moment arm is almost never easy to see. The cross product computes the full moment about a point from coordinates alone, and a dot product then extracts the part that turns a body about a hinge or shaft.
In this topic
- Beyond the page
- The cross-product moment
- Components of the moment
- Three rules for r × F
- Worked example: a cable on a post
- Reading the components
- Moment about an axis
- Two ways to compute it
- Worked example: a hinged hatch
- When the moment about an axis is zero
- Common mistakes to avoid
- Key takeaways
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