Geometry and Spatial Sense, Grades 4 to 6 - EduGains

6
Perpendicularity Perpendicularity is a concept that
develops in the later junior grades.
Edges and faces can often be
described as “at right angles” to other
faces and edges.
PRISM PROPERTIES
Geometry and Spatial Sense, Grades 4 to 6
The base of
this rectangular
prism is
perpendicular
to the vertical
faces.
The base of this
prism is not
perpendicular to
its vertical faces..
There are different formal and informal definitions of prisms. Despite the varying definitions,
there is little disagreement as to what a prism is. Students recognise which solids are prisms
and usually use common descriptions – for example, “a solid with two bases that are the
same size and shape”. Essentially, this definition clearly describes prisms; it is the role of the
teacher to guide students to the richer descriptions that include more complex geometric
concepts. An accepted definition of a prism is the following:
A prism is a solid geometric figure whose two ends are parallel and congruent polygons,
called bases. Lines joining corresponding points on the bases are always parallel. The sides of
prisms are always parallelograms.
If the vertical edges of the prism are perpendicular to the edges of the base, the prism is
described as a right prism. When the edges do not run perpendicular to each other, the
prism is said to be an oblique prism.
The ends of this prism are congruent triangles. These
ends (surfaces) are known as the bases of the prism.
The vertices of the bases are connected by parallel lines,
known as edges.
Right prism Oblique prism