Year 7 Interactive Maths - Second Edition

Polyhedra and Prisms

Polyhedra

A polyhedron (or planer body) is a solid or hollow body that is made up entirely of plane faces and is three-dimensional.

For example, a cuboid is a polyhedron as it is entirely made up of planes.  Planes that make up the cuboid are called its faces.  There are six faces of the cuboid.

The plural of polyhedron is polyhedra.  In Greek, poly means many and hedra means base.

A polyhedron is named after its number of faces.  Some polyhedra and their names are shown below.

A pentahedron has five faces, a hexahedron has six faces and a decahedron has 10 faces.

Other examples of polyhedra are:

Prisms

A prism is a solid with cross-sections that are parallel to its base.

The following solid is a prism.

A prism is named according to the shape of the its base (i.e. shape of its cross-section).  So, the solid drawn above is an example of triangular prism.

Some other prisms are drawn below:

Key Terms

polyhedron, polyhedra, cuboid, faces, tetrahedron, heptahedron, enneahedron, octahedron, pentahedron, hexahedron, decahedron, dodecahedron, icosahedron, prism, cross-section, triangular prism, rectangular prism, hexagonal prism, pentagonal prism