Lesson video

Hi, I'm Mr Bond, and in this lesson, we're going to learn how to identify, label and count faces, edges and vertices.

Let's start by thinking about a cuboid.

We need to be able to identify the faces, the edges and the vertices.

Let's start by thinking about the vertices.

Vertices is the plural of vertex.

A vertex, you might think of as the corners of the shape.

This is where two or more line segments meet.

So here are some examples of the vertices.

Now lets' think about the edges.

The edges are the line segments that run between two vertices.

So here are some examples of edges on a cuboid.

And the faces are the flat surfaces, so here are some examples of the faces.

Here's another shape, a square based pyramid.

Could you draw some arrows to the vertices, edges and faces of this shape? Here are two examples of vertices, here are some edges, and here are two arrows pointing at two of the faces, the square base and one of the triangular sides.

We're often asked to count the number of edges, faces or vertices in a shape.

Let's have a think about this.

Elliot says that a cube has three faces, he demonstrates this by numbering the faces on a diagram, and you can see that diagram to the right hand side.

Pause the video and have a think, do you agree with Elliot? Resume the video when you've finished.

Of course, we should disagree with Elliot.

We're only looking at this cube from one perspective, let's think about the net of this cube.

If we draw out the net, it would look like this, and now we can clearly see that this would have six faces.

Here are some questions for you to try, pause the video to complete the task and resume the video once you've finished.

Here are the answers.

The flat surfaces of 3D shapes are faces, a line segment joining two vertices of a 3D shape is called an edge, and the corners of a 3D shape where two or more line segments meet are called vertices.

Hopefully you managed to label those correctly on the cuboid underneath.

As I mentioned earlier, we're very often asked to find the number of faces, edges and vertices for a particular shape.

In this example, we're asked to find the number of faces, edges and vertices in a triangular prism.

Let's start by counting the number of edges that we can see on this diagram.

We can see one, two, three, four, five, six edges, and now let's count the vertices.

We can see one, two, three, four, five vertices.

We can also see two faces, so is that the answer? Two faces, six edges and five vertices? No, of course not, we're almost making the mistake that Elliot made in our previous example.

We need to realise that there are some of the faces, edges and vertices that we can't see.

Here's a diagram to help us out.

Pause the video to see if you can find the number of faces, edges and vertices in this diagram.

Hopefully you've spotted five faces, nine edges and six vertices.

Here's another question for you to try.

Pause the video to complete the task and resume the video when you've finished.

Here are the answers, hopefully if you were using pictures or sketches of those 3D shapes, you realised that there might be some faces, edges and vertices that you can't see.

It would be really helpful if you had the actual 3D shapes with you.

Then, you needed to think, is there a link between the number of edges, faces and vertices? And hopefully some of you found that the number of edges is equal to the number of faces add the number of vertices subtract two.

That's all for this lesson, thanks for watching.