The idea, step by step
State the rule
A useful rule is “has a curved surface” or “has only flat faces”. State the rule so someone else can repeat your sorting.
Sorting by colour can be useful, but it does not explain the shape. Flat faces, curved surfaces and corners describe the solids themselves.
An object may fit two groups
A cylinder has flat faces and a curved surface. If the groups are “has flat faces” and “has a curved surface”, it belongs in both.
For groups that must not overlap, try “only flat surfaces” and “has any curved surface”. Check every object against the exact wording.
A common trap
Assuming an object can have only one kind of surface.
Instead: Look for all its features before sorting.
See the thinking
Only flat faces
Which pictured objects have only flat faces?
- A is a cube and D is a rectangular box.
- B and C include curved surfaces.
Both features
Can a cylinder fit “has flat faces” and “has a curved surface”?
- Its two ends are flat circles.
- Its side is curved.
Check your understanding
Do both a cube and a cylinder have flat faces?
Show answer
Yes
A cube has six flat faces; a cylinder has two.
Your turn
6 questions · Work at your own pace.
Read the questions online
- List the labelled objects with a curved surface.
- Which labelled object has no flat faces?
- A cube and rectangular box are grouped together. Suggest a shape rule that fits both.
- A sphere and cylinder are grouped because they can roll. Is that a sensible rule? Explain.
- Give a feature that separates a sphere from a cylinder.
- Sort cube, cylinder and sphere into “only flat surfaces” and “has a curved surface”.
Read the worked solutions
- List the labelled objects with a curved surface.
The cylinder and sphere have curved surfaces.
B and C. - Which labelled object has no flat faces?
C is a sphere.
C. - A cube and rectangular box are grouped together. Suggest a shape rule that fits both.
Other correct shared-feature rules, such as both have corners, are acceptable.
Example: both have only flat faces. - A sphere and cylinder are grouped because they can roll. Is that a sensible rule? Explain.
Both have a curved surface.
Sharing a feature does not make the solids identical.
Yes, if the rule is rolling on a curved surface. - Give a feature that separates a sphere from a cylinder.
Both have curved surfaces, so that feature would not separate them.
The cylinder has flat faces; the sphere has none. - Sort cube, cylinder and sphere into “only flat surfaces” and “has a curved surface”.
This rule places each object in one group.
Only flat surfaces: cube. Has a curved surface: cylinder and sphere.
Curriculum reference & lesson scope
Australian Curriculum v9 and SA Curriculum
Solid-object features; comparing/classifying objects; turns; smaller/larger than a right angle.
Official curriculum source ↗