Concept
Line of action
2 essays name this object, across one field. What follows is each of them, and the objects they name alongside it.
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 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 diagramConcurrencyDeterminacyForce equilibriumForce polygonFunicularGraphic staticsIndependent equationsMoment centreMoment equilibriumResultantRigid body