1.3 2D and 3D shapes

‘2D’, or ‘two-dimensional’, simply means that the shape is flat. We can draw 2D shapes on paper. Common examples are shown in Figure 5.

Figure 5 2D shapes

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Six illustrations of 2D shapes: a circle, square, rectangle, pentagon, triangle and hexagon.

Figure 5 2D shapes

A ‘3D’ (‘three-dimensional’) shape is a solid shape. It has three dimensions, that is, length, width and depth. An easy way of thinking about the difference between a 2D and a 3D shape is to think ‘If I shone a torch on the shape, would it have a shadow?’ 3D shapes cast a shadow but 2D shapes don’t.

Obviously the screen that you’re reading this on is 2D, so 3D shapes are represented using shading.

Figure 6 A 2D and 3D shape

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An illustration of a circle (2D) and a sphere (3D).

Figure 6 A 2D and 3D shape

Activity 3: 2D or 3D?

Say if the following shapes are 2D or 3D:

Which shapes in Figure 7 are 2D and which are 3D?

Figure 7 2D and 3D shapes

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Six illustrations of 2D and 3D shapes.

Figure 7 2D and 3D shapes

Answer

Shapes (a), (c) and (e) are 2D.

Shapes (b), (d) and (f) are 3D.