Motion of an object where the path of every point is a circle or circular arc. A rotation is defined by a point and vector which determine the axis of rotation. The direction of the vector is the direction of the axis and the magnitude of the vector is the angle of rotation. Stress acting parallel to an imaginary plane cut through an object. Strain measuring the intensity of racking in the material.
Shear strain is measured as the change in angle of the corners of a small square of material.
Stability is best defined as the opposite of instability, which is the occurrence of large structural deformations which are not the result of material failure. In a statically determinate structure, internal forces and reactions can be determined by considering nothing more than equations of equilibrium. High stiffness means that a large force produces a small displacement. The intensity of deformation at a point in an object. See normal strain and shear strain .