| Shear stress: | (english) Stress acting parallel to an imaginary plane cut through an object. |
| Shear strain: | (english) 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. |
| Shear modulus: | (english) The ratio of shear stress divided by the corresponding shear strain in a linear elastic material. |
| Stability: | (english) 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. |
| Static equilibrium: | (english) Equilibrium which does not include inertial forces. |
| Statically determinate: | (english) A statically determinate structure is one where there is only one distribution of internal forces and reactions which satisfies equilibrium. In a statically determinate structure, internal forces and reactions can be determined by considering nothing more than equations of equilibrium. |
| Statically equivalent: | (english) Two force systems are statically equivalent when their resultants are equal. Physically, this means that the force systems tend to impart the same motion when applied to an object; note that the distribution of resulting internal forces in the object may be different. |
| Statically indeterminate: | (english) A statically indeterminate structure is one where there is more than one distribution of internal forces and/or reactions which satisfies equilibrium. |
| Stiffness: | (english) This is a general term which may be applied to materials or structures. When a force is applied to a structure, there is a displacement in the direction of the force; stiffness is the ratio of the force divided by the displacement. High stiffness means that a large force produces a small displacement. When discussing the stiffness of a material, the concept is the same, except that stress substitutes for force, and strain substitutes for displacement; see modulus of elasticity. |
| Strain: | (english) The intensity of deformation at a point in an object. See normal strain and shear strain. |