A catenoid is a type of surface in topology, arising by rotating a catenary curve about an axis. It is a minimal surface, meaning that it occupies the least area when bounded by a closed space. It was formally described in 1744 by the mathematician Leonhard Euler.
Soap film attached to twin circular rings will take the shape of a catenoid. Because they are members of the same associate family of surfaces, a catenoid can be bent into a portion of a helicoid, and vice versa.
The dome shape of Inuit igloos can be derived from rotation of a catenary about its central axis.
The catenoid was the first non-trivial minimal surface in 3-dimensional Euclidean space to be discovered apart from the plane. The catenoid is obtained by rotating a catenary about its directrix. It was found and proved to be minimal by Leonhard Euler in 1744.[non-primary source needed]
Early work on the subject was published also by Jean Baptiste Meusnier.[non-primary source needed] There are only two minimal surfaces of revolution (surfaces of revolution which are also minimal surfaces): the plane and the catenoid.
The catenoid may be defined by the following parametric equations:
- where and and is a non-zero real constant.
In cylindrical coordinates:
- where is a real constant.
A physical model of a catenoid can be formed by dipping two circular rings into a soap solution and slowly drawing the circles apart.
The catenoid may be also defined approximately by the Stretched grid method as a facet 3D model.
Because they are members of the same associate family of surfaces, one can bend a catenoid into a portion of a helicoid without stretching. In other words, one can make a (mostly) continuous and isometric deformation of a catenoid to a portion of the helicoid such that every member of the deformation family is minimal (having a mean curvature of zero). A parametrization of such a deformation is given by the system
- for , with deformation parameter ,
where corresponds to a right-handed helicoid, corresponds to a catenoid, and corresponds to a left-handed helicoid.
The Inuit learned to pattern the structure of their igloos, or snow houses, after a shape with a catenary arch cross-section, which offers an optimal balance between height and diameter, avoiding the risk of collapsing under the weight of compacted snow. This differs from what is normally called a catenoid in that the catenary is rotated about its central axis, forming a surface with the topology of a bowl rather than that of a cylinder.
- Dierkes, Ulrich; Hildebrandt, Stefan; Sauvigny, Friedrich (2010). Minimal Surfaces. Springer Science & Business Media. p. 141. ISBN 9783642116988.
- Gullberg, Jan (1997). Mathematics: From the Birth of Numbers. W. W. Norton & Company. p. 538. ISBN 9780393040029.
- Helveticae, Euler, Leonhard (1952) [reprint of 1744 edition]. Carathëodory Constantin, ed. Methodus inveniendi lineas curvas: maximi minimive proprietate gaudentes sive solutio problematis isoperimetrici latissimo sensu accepti (in Latin). Springer Science & Business Media. ISBN 3-76431-424-9.
- Meusnier, J. B (1881). Mémoire sur la courbure des surfaces [Memory on the curvature of surfaces.] (PDF) (in French). Bruxelles: F. Hayez, Imprimeur De L'Acdemie Royale De Belgique. pp. 477–510. ISBN 9781147341744.
- "Catenoid". Wolfram MathWorld. Retrieved 15 January 2017.
- Handy, Richard L. (Dec 1973). "The Igloo and the Natural Bridge as Ultimate Structures" (PDF). Arctic. Arctic Institute of North America. 26 (4): 276–281. doi:10.14430/arctic2926.
The Eskimo snow igloo is not a hemisphere as frequently depicted, but a catenoid of revolution with an optimum height-to-diameter ratio. This shape eliminates ring tension and shell moments and therefore prevents failure by caving or bulging.
- Krivoshapko, Sergey; Ivanov, V. N. (2015). "Minimal Surfaces". Encyclopedia of Analytical Surfaces. Springer. ISBN 9783319117737.