non-automatic technique for doing the same thing. Examples Engineering Stiction refers to the characteristic of start-and-stop–type motion of a mechanical assembly. Consider a mechanical element slowly increasing an external force on an assembly at rest that is designed for the relative rotation or sliding of its parts in contact. The static contact friction between the assembly parts resists movement, causing the spring moments in the assembly to store mechanical energy. Any part of the assembly that can elastically bend, even microscopically, and exert a restoring force contributes a spring moment. Thus the "springs" in an assembly might not be obvious to the eye. The increasing external force finally exceeds the static friction resisting force, the spring moments, released, impulsively exert their restoring forces on both the moving assembly parts and, Newton's Third Law, in reaction on the external forcing element. The assembly parts then impulsively accelerate in motion with respect to each other though resisted by dynamic contact friction (in this context very much less than the static friction). However, the forcing element cannot accelerate at the same pace, fails to keep up and loses contact. The external force on the moving assembly momentarily drops to zero for lack of forcing mechanical contact even though the external force element continues its motion. The moving part then decelerates to a stop from the dynamic contact friction. The cycle repeats as the forcing element motion catches up to contact again. Stick, store spring energy, impulsively release spring energy, accelerate, decelerate, stop, stick. Repeat. Stiction is a problem for the design and materials science of many moving linkages. This is particularly the case for linear sliding joints, rather than rotating pivots. Owing to simple geometry, the moving distance of a sliding joint in two comparable linkages is longer than the circumferential travel of a pivoting bearing, thus the forces involved (for equivalent work) are lower and stiction forces become proportionally more significant. This issue has often led to linkages being redesigned from sliding to purely pivoted structures, just to avoid problems with stiction. An example is the Chapman strut, a suspension linkage. Surface micromachining During surface micromachining, stiction or adhesion between the substrate (usually silicon-based) and the microstructure occurs during the isotropic wet etching of the sacrificial layer. The capillary forces due to the surface tension of the liquid between the microstructure and substrate during drying of the wet etchant cause the two