1
Sorting solid shapes
Discover Mathematics P2: Term 1, Lessons 41–50
GoalSort solid shapes with rules about faces, vertices and curved surfaces.
New words
rule · a sentence that tells which solids belong togethercurved surface · a round side that is not flatcircle face · a flat face shaped like a circlefit · follow the rule
Explanation
To sort solids we use a rule. First learn what each solid has. Look at the table: the cube and the box have 6 flat faces and 8 vertices. The pyramid has 5 faces and 5 vertices. The cylinder has 2 flat circle faces and no vertices. The cone has 1 circle face and 1 vertex. The sphere has no flat face and no vertex. A rule such as ‘has a circle face’ fits the cylinder and the cone. A rule such as ‘has no vertices’ fits the cylinder and the sphere.
| Solid | Flat faces | Vertices |
|---|---|---|
| cube | 6 | 8 |
| box | 6 | 8 |
| pyramid | 5 | 5 |
| cylinder | 2 | 0 |
| cone | 1 | 1 |
| sphere | 0 | 0 |
Worked examples
| Solid | Circle face? |
|---|---|
| cube | no |
| cylinder | yes |
| cone | yes |
Rule: has no vertices. The sphere fits because it is round all over.
Rule: has 6 or more faces. A box has 6 flat faces, so it fits. A pyramid has only 5, so it does not.
Class activity
Sort the kitchen. Gather things shaped like solids: a tin, a box of tea, a ball, a funnel, a block of cheese. Make two piles with a secret rule such as ‘has a circle face’. The other person guesses the rule. Then switch.
Practice
1
Rule: has 8 vertices. Which solids fit?
The cube and the box.
2
Does this solid fit the rule ‘exactly 1 vertex’?
Yes. It is a cone, and it has 1 vertex.
3
Mina says the cylinder fits both rules ‘has a circle face’ and ‘has no vertices’. Is she right?
Yes. It has 2 circle faces and no vertices.
4
Make up a rule that fits the cube and the box but not the sphere.
For example: ‘has flat faces’ or ‘has 8 vertices’.
5
Which solid does NOT fit ‘has a curved surface’: cube, cone or sphere?
The cube. All its faces are flat.