Mathematics K–6 · Years 3–4
Skeleton models: faces, edges and vertices
Measurement and space
The idea
A prism or pyramid can be built from edges and corners alone, and counting the faces, edges and vertices of each model identifies its key features and lets different objects be compared.
What you need
- 60 wooden skewers with the points removed (or straws): 40 cut to 8 cm and 20 cut to 12 cm
- 40 small balls of modelling clay or plasticine (about 1.5 cm)
- a set of solid prisms and pyramids to copy
- a recording table with columns object, faces, edges, vertices
How to do it
- Copy a cube: join skewers with clay balls at the corners. Count the clay balls (vertices), the skewers (edges) and the open frames (faces).
- Build a triangular prism and a square pyramid the same way, counting each time.
- Build a rectangular prism that is not a cube and compare its counts with the cube.
- Compare the rows of the table: find the two models with the same counts and the two with the same number of faces, and say what is different about each pair.
- Sketch each model and draw a net for the cube on grid paper, checking it folds by cutting it out.
What you should see
The cube has 6 faces, 12 edges and 8 vertices; the triangular prism 5, 9 and 6; the square pyramid 5, 8 and 5; the rectangular prism the same counts as the cube. The cube and the rectangular prism share their counts although their faces differ in shape, and the triangular prism and the square pyramid both have 5 faces but differ in edges (9 and 8) and vertices (6 and 5). A net of six squares in a cross folds into the cube, and the pair can name which squares become opposite faces.
What changes
This activity lists no variables to change, measure and keep the same.
Common misconceptions
Each of these ideas is wrong, and the activity is a chance to test it.
- A cube has 4 faces because that is what you can see from one side.
- A pyramid always has a square base.
Safety card
Hazards
- skewer points
- plasticine on clothing
Controls
- cut the points off skewers before the lesson; work on a mat
Note
No chemicals or heat are used, so the NSW Department of Education Chemical Safety in Schools package is not needed; ordinary classroom supervision under the school's usual risk management.
Curriculum references
The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.
- Mathematics K-10 Syllabus (2022), NSW Education Standards AuthorityMA2-3DS-01MAO-WM-01
- Australian Curriculum v9AC9M3SP01
Sources
The pages the author read to write this activity.