Resultant
Three forces must meet at a point, and a drawing can find it
A body held by exactly three forces has their lines of action concurrent. That is a theorem, it is enough to solve for direction and magnitude, and for a century it was done with a straightedge.
The load that is spread out, and the force that replaces it
A distributed load can be swapped for a single force at its centroid. The reactions come out identical and the bending moment does not, and knowing which side of the cut the swap is legitimate on is most of the skill.
The train that is worse than its heaviest axle
An influence line says where to stand one load. A vehicle is several loads at fixed spacings, and the worst arrangement never puts the heaviest one at the peak.
Named alongside it
The objects these essays reach for when they reach for this one.
Free body diagramAxle trainBarre ruleBending momentCentroidConcurrencyDistributed loadForce polygonFunicularGraphic staticsIdealisationInfluence line