Ringikujuline

Ringikujuline is an Estonian adjective that translates to ring-shaped or annular in English. It describes objects or figures that have the form of a ring, typically featuring a central void bounded by an outer boundary that is circular in outline.

In geometry, the most common ring-shaped figure is the annulus: the region of points in a plane whose distance from a fixed center lies between two concentric circles with radii r and R, where 0 < r < R. If the inner radius r is zero, the ring degenerates to a disk.

Properties include that the area of a ringikujuline region is A = π(R^2 − r^2). The boundary consists of two circles: the outer circumference 2πR and the inner circumference 2πr. The shape is characterized by its hole, which distinguishes it from a solid disk.

Applications span various fields. In engineering and manufacturing, ringikujuline components such as washers, spacers, or gaskets distribute loads, separate parts, or seal gaps. O-rings are another widely used ring-shaped element. In design and jewelry, rings and ring-shaped decorative elements are common, as are filters and certain mechanical seals that rely on annular geometries.

Examples of usage include describing a flat, ring-shaped washer or identifying an annular cross-section in mechanical parts. See also annulus, circular ring, and torus for related geometric concepts. The term underscores a specific planar form that emphasizes a central void within a circular boundary.