Square pyramid

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Square pyramid
Square pyramid.png
Type Johnson
J92J1J2
Faces 4 triangles
1 square
Edges 8
Vertices 5
Vertex configuration 4(32.4)
(34)
Schläfli symbol ( ) ∨ {4}
Symmetry group C4v, [4], (*44)
Rotation group C4, [4]+, (44)
Dual polyhedron self
Properties convex
Net
Square pyramid net.svg

In geometry, a square pyramid is a pyramid having a square base. If the apex is perpendicularly above the center of the square, it is a right square pyramid, and has C4v symmetry. If all edges are equal, it is an equilateral square pyramid,[1] the Johnson solid J1.

General square pyramid[edit]

A possibly oblique square pyramid with base length l and perpendicular height h has volume:

.

Right square pyramid[edit]

In a right square pyramid, all the lateral edges have the same length, and the sides other than the base are congruent isosceles triangles.

A right square pyramid with base length l and height h has surface area and volume:

.

The lateral edge length is:

,

and the slant height is:

.

The dihedral angles are:

between the base and a side: ;
between two sides: .

Equilateral square pyramid, Johnson solid J1 [edit]

If all the edges have the same length, then the sides are equilateral triangles, and the pyramid is an equilateral square pyramid, Johnson solid J1.

The Johnson square pyramid can be characterized by a single edge-length parameter l. The height h (from the midpoint of the square to the apex), the surface area A (including all five faces), and the volume V of such a pyramid are:

Graph[edit]

A square pyramid can be represented by the Wheel graph W5.

Related polyhedra and honeycombs[edit]

Square bipyramid.png Tetrakishexahedron.jpg Usech kvadrat piramid.png
A regular octahedron can be considered a square bipyramid, i.e. two Johnson square pyramids connected base-to-base. The tetrakis hexahedron can be constructed from a cube with short square pyramids added to each face. Square frustum is a square pyramid with the apex truncated.

Square pyramids fill space with tetrahedra, truncated cubes or cuboctahedra.[2]

Dual polyhedron[edit]

The square pyramid is topologically a self-dual polyhedron. The dual edge lengths are different due to the polar reciprocation.

Dual Square pyramid Net of dual
Dual square pyramid.png Dual square pyramid net.png

References[edit]

  1. ^ Franz Hocevar, Solid Geometry, 1903, p. 44
  2. ^ http://woodenpolyhedra.web.fc2.com/JohnsonHoneycomb.pdf

External links[edit]