Serration

The serrated edges of tiger shark teeth.

A hunting knife] with a serrated back edge.

Serrated leaves of the nettle, Urtica dioica.

Serration generally refers to a saw-like appearance or a row of sharp or tooth-like projections. A serrated cutting edge has many small points of contact with the material being cut. By having less contact area than a smooth blade or other edge, the applied force at each point of contact is relatively greater and the points of contact are at a sharper angle to the material being cut. This causes a cutting action that involves many small splits in the surface of the material being cut, which cumulatively serve to cut the material along the line of the blade.

Serration is common both in nature and in man-made objects. In nature, serration is commonly seen in the cutting edge on the teeth of some species, usually sharks. However, it also appears on non-cutting surfaces, for example in botany where a toothed leaf margin or other plant part is described as being serrated. Just as the serrated edge of a knife provides many small points of entry from which to apply a concentrated cutting force, a serrated leaf edge provides a more concentrated force against wind and other natural elements.

Human uses of serration have copied those found in nature. For example, a notch on a saw or other serrated blade serves the same cutting purpose as the serration of an animal tooth. Serration also appears in the profile of a screw thread cross section in extrusion. The feature is also found in airframe shapes used in certain stealth aircraft, which use the jaggedness of the serrated edge to confuse radar signals.