sivupinnan

Sivupinnan, from Finnish sivu meaning side and pinta meaning surface, is a geometric term used to denote the lateral or side surface of a three-dimensional solid. It refers to the portion of the object's surface that connects its end faces, excluding the base or top faces. The concept is central in calculating lateral surface area, which is the area of the sides only.

In common solids, sivupinta varies by shape. For a right circular cylinder, the sivupinta is the curved cylindrical surface with area 2πrh, where r is the radius and h the height. For a rectangular prism or box, the sivupinnat consist of the four vertical faces, and the total sivupinta equals the perimeter of the base times the height, i.e., 2h(a+b). For a right circular cone, the sivupinta is the curved surface excluding the base, with area πrl, where l is the slant height. For pyramids, the sivupinta comprises the lateral faces, with area equal to the sum of these faces.

The term is used in mathematics, engineering, and design to discuss materials, coating, and thermal or aerodynamic properties. It is distinct from the end surfaces (bases or ends) and from the total surface area, which combines all faces.