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SESK: Stuff Everyone Should Know · sesk.info/eng-moment-force-through-pivot

A force's line of action passes right through the pivot. What moment does it make about that pivot?

Zero: the moment arm is zero, so the moment is zero.

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  1. Its full force times the bar length
  2. Half its force times the bar length
  3. Zero ✔

Why: Moment equals force times the perpendicular distance from the pivot to the force's line of action. If the line goes through the pivot, that distance is zero.

Huh, didn't know that: You can slide a force along its own line of action without changing its moment about any point.

The dad joke
I pushed on the door right at the hinge for an hour. Zero moments of progress.
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References

Answer: Zero. Moment equals force times the perpendicular distance from the pivot to the force's line of action. If the line goes through the pivot, that distance is zero.

  1. Engineering Statics (Baker and Haynes): 4.1 Moment of Force engineeringstatics.org/moment-of-force.html
    If the point lies upon the force's line of action, then the moment arm is zero, making the moment zero as well.
    Checked 2026-10-10.

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