Prisms and Cylinders

Solids whose congruent faces sit facing each other at top and bottom are sorted into prisms and cylinders. Names come from the shape of the base, giving triangular, quadrilateral and pentagonal prisms, and the counts of vertices, edges and faces are worked out by tying them to the number of corners on the base.

Answering 5 for the number of faces on a pentagonal prism, without counting the two bases, stands out. For edges, doubling only the base edges and dropping the vertical edges of the sides gives 10 instead of 15, which is typical. Confusing a base with a side face, and misreading a figure drawn lying on its side, also occurs.

Following Circles and Regular Polygons, this unit takes up prisms and cylinders as solids, counting vertices, edges and faces from the shape of the base. This experience of counting a solid's faces connects into grade 6, when Surface Area of Solids calculates the surface of a triangular prism or a cylinder.