Who would have thought that the properties of the cone and cylinder would cause such a stir in the Teach Starter office? But, they certainly did some time ago! As teachers, a lot of us taught our young students that cones and cylinders have edges and faces. Anyone else?
However, this is no longer the case and there is a mathematical reason behind this change!
Why Do Cylinders and Cones Not Have Edges or Faces?
As teachers, we thought the best place to look to clear up the debate would be the Australian curriculum. However, like a lot of sites, it wasn’t very clear why cones and cylinders do not have edges or faces.
We found the NSW syllabus outlines the language that should be used the classroom around this topic to be very clear, Hence, we are using this as our source of information:
- In geometry, the term ‘face’ refers to a flat surface with only straight edges, as in prisms and pyramids, eg. a cube has six faces.
- Curved surfaces, such as those found in cylinders, cones, and spheres, are not classified as ‘faces’.
- Similarly, flat surfaces with curved boundaries, such as the circular surfaces of cylinders and cones, are not ‘faces’.
- In geometry, the term ‘edge’ refers to the interval (straight line) formed where two faces of a three-dimensional object meet.
- The NSW Syllabus describes a cylinder as a 3D object that has two flat surfaces, one curved surface, no faces, no edges and no vertices.
It’s really important that children grasp the difference between prisms, pyramids, cubes and cones, cylinders and spheres. By understanding the mathematical definitions of the language used to describe the properties of 3D objects, your students are being set up for success.
Resources to get you started:
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Thank you for this valuable information and for updating your resources. I had no idea that the syllabus had changed.
No problem, Lorraine! Thank you for the comment, we're here to help!
Hello, So if cylinders and cones do not have an edge what do you call that part where the two sides meet?? It exists therefore needs a name. And what do you call the circular face if only a face has straight sides? Thanks Raylene
Hi Raylene, A 'circular face' is referred to as a flat surface in the NSW syllabus. As for the 'edges' of cones and cylinders, the NSW syllabus doesn't explicitly state what they are called. It refers to the objects' circular faces as having curved boundaries, but does give a name to their 'curved edges'. Naming this type of feature could be a fun activity for your students! Have them come up with a cool new name and pitch it to the class.