Triangular prism

A triangular prism has six vertices, nine edges, and five faces. Every prism has two congruent faces known as its bases, and the bases of a triangular prism are triangles. The triangle has three vertices, each of which pairs with another triangle's vertex, forming three edges. These edges form three parallelograms as other faces. It is also considered a special case of a wedge, a polyhedron with two triangular and three trapezoidal faces. A triangular prism can have the form of a right prism, meaning that its edges are perpendicular to the base, forming rectangular-shaped lateral faces. Like any-sided prism, it has all vertices lying on the parallel bases, a prismatoid.

The vertices and edges of a triangular prism can give rise to a graph. This is due to Steinitz's theorem, stating that any convex polyhedron can be drawn into a planar graph that is 3-connected, meaning the edges of a graph do not cross each other, and the vertices are impossible to disconnect whenever picking any two vertices to be removed. Classifying into a family, the graph of a triangular prism is the prism graph Π₃, where the symbol Π_n represents the graph of an n-sided prism. The graph of a triangular prism is a type of planar graph formed from a tree with no degree-two vertices by adding a cycle connecting its leaves, an example of Halin graph.

As a uniform prism

When all edges are equal in length, its bases and its lateral faces are all equilaterals and squares, respectively. Hence, the triangular prism is semiregular. A semiregular prism means that the number of its polygonal base's edges equals the number of its square faces. More generally, the triangular prism is uniform. This means that a triangular prism has regular faces and has a symmetry of mapping any two vertices known as isogonal. The dihedral angle between two adjacent square faces is the internal angle of an equilateral triangle π/3 = 60°, and that between a square and a triangle is π/2 = 90°.

The volume of any prism is the product of the area of the base and the distance between the two bases. In the case of a triangular prism, its base is a triangle. The area of a triangle is the half product of its base b and its height h, formulated as ⁠1/2⁠bh. Since the triangular prism has a distance l between two triangular bases, the general formula for its volume is: In the case of a right triangular prism, where all its edges are equal in length l, its volume can be calculated as the product of the equilateral triangle's area and the distance between bases:

The three-dimensional symmetry group of a triangular prism is prismatic symmetry D_3h of order 12: the appearance is unchanged if the triangular prism is rotated one- and two- thirds of a full angle around its axis of symmetry passing through the center's base, and reflecting across a horizontal plane. The dual polyhedron of any prism is a bipyramid, a polyhedron formed by fusing two pyramids base-to-base. In the case of a triangular prism, its dual is a triangular bipyramid, both of which have a common three-dimensional symmetry group.

A triangular prism is commonly designed as a transparent optical object to disperse light. The cluster of a chemical compound known as trigonal prismatic molecular geometry resembles the structure of a triangular prism, with an example compound being hexamethyltungsten. In architecture, an example of a building with a triangular prism shape is Flatiron Building in New York City. An instance of food that resembles the shape of a triangular prism is a Swiss chocolate brand of Toblerone.

Honeycomb and tiling

The uniform triangular prism is a plesiohedron, a space-filling polyhedron that can be defined as the Voronoi cell of a symmetric Delone set in order to create a honeycomb. The triangular prismatic honeycomb is an example where triangular prisms are the only prototiles. The other honeycombs with a cell being triangular prism and other polyhedra are gyroelongated alternated cubic honeycomb (with regular octahedra and tetrahedra), elongated alternated cubic honeycomb (with regular octahedra and tetrahedra), snub square prismatic honeycomb, triangular-hexagonal prismatic honeycomb, truncated hexagonal prismatic honeycomb, rhombitriangular-hexagonal prismatic honeycomb, snub triangular-hexagonal prismatic honeycomb, elongated triangular prismatic honeycomb.

John Horton Conway and Charles Radin in 1998 introduced the quaquaversal tiling, a three-dimensional non-periodic tiling. The prototiles are the 30-60-90 right triangular prisms, some of which are rotated π/3 and the others are rotated π/2 in a perpendicular direction.

In the construction of polyhedra

Beyond the triangular bipyramid as its dual polyhedron, many other polyhedra are related to the triangular prism. A Johnson solid is a convex polyhedron with regular faces, and this definition sometimes omits uniform polyhedra such as Archimedean solids, Catalan solids, prisms, and antiprisms. There are six Johnson solids with their construction involving the triangular prism:

• The elongated triangular pyramid and the elongated triangular bipyramid are made by attaching tetrahedron onto the base of a triangular prism.
• The augmented triangular prism, the biaugmented triangular prism, and the triaugmented triangular prism are constructed by attaching equilateral square pyramids onto the square face of the prism.
• The gyrobifastigium is constructed by attaching a triangular prism quarter-turn along to any square face of another one. It can tile a space of gyrated triangular prismatic honeycomb. Unlike the triangular prism, which is a plesiohedron, the gyrobifastigium is a stereohedron, because the points at the centers of the cells of its face-to-face tiling (where they are forced to go by symmetry) have differently-shaped Voronoi cells. If the gyrobifastigium has isosceles right triangles and silver rectangles, then it is a plesiohedron.

One can cut the part of a triangular prism at an oblique angle. The result has two bases that are not parallel, such that every distance between those bases has a different edge length. If the edges connecting bases are perpendicular to one of its bases, this prism can have a version of a right triangular prism. Given that A is the area of the triangular prism's base, and the three heights h₁, h₂, and h₃, its volume can be determined in the following formula:

Schönhardt polyhedron is another polyhedron constructed from a triangular prism with equilateral triangle bases. This way, one of its bases rotates around the prism's centerline and breaks the square faces into skew polygons. Each square face can be re-triangulated with two triangles to form a non-convex dihedral angle. As a result, the Schönhardt polyhedron cannot be triangulated by a partition into tetrahedra. It is also that the Schönhardt polyhedron has no internal diagonals. It is named after German mathematician Erich Schönhardt, who described it in 1928, although artist Karlis Johansons exhibited the related structure in 1921.

The triangular prism can be rectified from the convex hull of its midpoints' edges. The resulting construction yields three square faces on the same planes as the square faces of the prism, two equilateral triangle faces on the planes of the triangular ends of the prism, and six more isosceles triangle faces. By giving rise to a graph, its dual forms another convex polyhedron called Herschel enneahedron.

The number of triangular prisms can be composed by sharing a common center. Four uniform compounds of triangular prisms, they are compound of four triangular prisms, compound of eight triangular prisms, compound of ten triangular prisms, compound of twenty triangular prisms.

Polytopes

The triangular prism is first in a dimensional series of semiregular polytopes. Each progressive uniform polytope is constructed vertex figure of the previous polytope. Thorold Gosset identified this series in 1900 as containing all regular polytope facets, containing all simplexes and orthoplexes (equilateral triangles and squares in the case of the triangular prism). In Coxeter's notation the triangular prism is given the symbol −1₂₁.