3.2.1—Moments

The moment of a force about a point is force × perpendicular distance from the point to the force line: M=Fd. Choose a sign convention, usually clockwise and anticlockwise, and keep it throughout.

For several forces, take moments about a convenient point so unknown reactions through that point have zero moment. Resolve angled forces before finding their perpendicular contribution.

A 20 N force acting 0.30 m from a pivot produces a 6.0 N m moment. A 10 N force on the opposite side at 0.60 m balances it if the senses are opposite.

Distance along the rod is not automatically the moment arm; use the perpendicular distance to the force line, and do not mix force and moment units.