An object is in equilibrium if the resultant of the system of forces acting on it has zero magnitude. See static equilibrium and dynamic equilibrium . External forces are sometimes called applied forces . A fixed connection is sometimes called a rigid connection or moment-resisting connection. Flexibility is the inverse of stiffness .
High flexibility means that a small load produces a large displacement.
Bending deformation, i.e., deformation by increasing curvature. A directed interaction between two objects that tends to change the momentum of both. A deformation of a structure or material under load is described as inelastic when the deformation remains after the load is removed. The term plastic is often used with the same meaning. The tendency of an object at rest to remain at rest, and of an object in motion to remain in motion.