Moment equilibrium
Everything adds to nothing, and that is the whole of statics
A structure that stays put obeys two statements — the forces on it sum to zero, and so do the moments. Every number in the subject comes out of those two sentences.
Answering one question without solving the rest
A truss of fifty members can be interrogated about one of them. Cut through three, take moments about the point where two of them meet, and the third falls out in a single line.
The equation that is not new, and the three that are
A plane free body yields exactly three independent equations. Most attempts at a fourth are one of the first three wearing different clothes — and on a beam under vertical load, one of the three is already saying nothing.
Named alongside it
The objects these essays reach for when they reach for this one.
Free body diagramForce equilibriumMoment centreRigid bodyChord forceDeterminacyIdealisationIndependent equationsLever armLine of actionMethod of sectionsPanel shear