Nets
Nets are the flat (2D) shapes that are then folded up to make a 3D shape.
The next time you’ve finished with a cardboard box, unfold it and see how the 3D shape is made. Cubes and cuboids are fairly straightforward – look out for more complicated (interesting!) shapes. (Hint: this is a great excuse to go out and buy a Toblerone. For research of course. See how that Triangular Prism is constructed. However, once you’ve unfolded the box, you might as well eat the chocolate …!)
Here’s an ‘interesting’ 3D shape. It’s a triangular prism (but looks a little different from a Toblerone. Why?) What would it’s net look like? Can you sketch it?
A 2D Picture of a 3D Cube
Have you ever noticed how the numbers are arranged on a dice?
Did you know that opposite faces of a dice add up to seven?
Here’s a net of a cube – visualize the net folding up to make a cube. Can you see how the pairs of opposite faces will add up to seven?
Teaching Tip
A big shout out must go to my excellent TA Nicky Moulton for coming up with this great idea.
Give the pupils a sheet with the eleven different nets that can be used to make a cube. (Before doing this, you could, and probably should, challenge you pupils to see how many different nets of a cube then can find. There are eleven. This exercise gives you a great opportunity to discuss rotations and reflections, ask questions like: “are those really different nets?” Introduce the word “Congruent” etc.)
You can click on this link to get a PDF with all the eleven nets of a cube.
Then get the pupils to add the numbers one to six to each net so that it would fold up to create a ‘correct’ dice – e.g. each pair of opposite faces would add up to seven. Encourage the pupils to visualise the net folding up, rather than actually folding it. A great activity that doesn’t involve any sums!