Concept
Mechanism
2 essays name this object, across one field. What follows is each of them, and the objects they name alongside it.
Counting the unknowns, and finding out whether statics can answer
Two equations per joint, one unknown per member, one per restraint. Subtract, and the sign of the answer says whether the structure is a mechanism, solvable, or beyond what equilibrium alone can settle.
The count that does not see it
A frame can have exactly as many unknowns as equations and fold up anyway. The count asks whether there are enough equations; it never asks whether they are different from one another.
Named alongside it
The objects these essays reach for when they reach for this one.
BracingCompatibilityCritical formDeterminacyEquilibrium matrixIndependent equationsIndeterminacyRank deficiencyRedundancyStatic determinacyStiffnessTriangulation