# Lesson video

In progress...

Hi everyone, I'm Miss Miles.

Welcome to our maths lesson, before we start a did you know fact.

Today's fact is, did you know it is believed that ancient Egyptians used complex maths such as algebra and arithmetic as far back as 3000 BC.

Okay, back to our maths lesson today.

For today's lesson, you will need a pencil, a piece of paper and a clear workspace.

In today's lesson, we will be describing the properties of 3D shape and when you're ready, let's get started.

Okay, on screen now there are two shapes.

I would like you to think about what's the same about them and what's different.

Pause your video there and have a think about it for me.

Okay, so I know that the shapes that we've got on screen are a cube and a square.

So let's have a think about our cube first, and so I've got a cube here with me.

Here is my cube, so I know that a cube has got 1, 2, 3, 4, 5, 6 square faces.

I know that a cube has got 1, 2, 3, 4, 5, 6, 7, 8 vertices, and I know it has got 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 edges.

And I know that the six faces we talked about are square faces.

Okay, so that's my cube.

Now I've also got a square on screen.

A square has four sides and four vertices, I know that my cube is three dimensional because I can hold it in my hands.

And I know that my square is two dimensional, because I cannot hold it in my hands.

It has two dimensions, it has length and width.

My cube is three dimensional because it has length, width and breadth.

One thing about them that is similar though, is that in my cube I've got square faces.

So my 2D square can help to make up the faces of my 3D shape.

Okay, let's move on.

So I've got a variety of 3D shapes on the screen now, and we are going to have a think about them, think about their properties and then I'm going to sort them.

So all of the different shapes on screen, I have got real ones here with me and we're going to have a look at them together.

So the first shape I can see is a cone, and I've got a cone here with me, here it is.

So I'm going to first of all identify the properties of my cone.

I know that my cone has got one flat face and one curved face, and then the point at the top is an apex.

There are no vertices and there is one edge, so that's my cone.

My second shape on screen is a cuboid.

Again, I have a cuboid here with me, I know that a cuboid has 1, 2, 3, 4, 5, 6 faces.

Four of the faces are rectangular, and two of the faces one at either end are square faces.

It has 1, 2, 3, 4, 5, 6, 7, 8 vertices, it has 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 edges.

They are the properties of my cuboid.

Next I have a square-based pyramid, again I've got one here with me.

My square-based pyramid has got a square face at the bottom and then 1, 2, 3, 4 triangular faces.

So it has five faces in total and it has got 1, 2, 3, 4, 5 vertices and it has 1, 2, 3, 4, 5, 6, 7, 8 edges.

That's the properties of my square-based pyramid.

Next, I have a cylinder.

Here's my cylinder, my cylinder has 1, 2, 3 faces.

It has a square face, a square face, a circle face at either end and then this face going round here is a curved face.

And it also has two edges, and it has no vertices.

And then last but not least, we have a sphere.

So here's my sphere, it has one curved face, no vertices, no edges.

I'm now going to sort the shapes, we've talked about their properties but how can I sort them? So we talked about their faces a lot, I've noticed that there are shapes that have flat faces, and there are shapes that have curved faces, and I can sort them by that criteria.

A 3D shape that has only flat faces is a polyhedron.

So I'm going to sort them into polyhedrons and non-polyhedrons.

So of the shapes on screen, my polyhedrons would be my cuboid and my square-based pyramid, because they have only flat faces.

And my non-polyhedrons would be my sphere, cone and cylinder because they have curved faces as well.

So they're not polyhedrons.

So let me show you that now, here we go.

This is how I've sorted them, so for the polyhedrons I've got my cuboid and I've got my square-based pyramid, and I've added my triangular prism in there as well as an additional one.

And then my non-polyhedrons are my cylinder, cone and sphere.

So that's how I would sort them.

I would like you to have a think about now, how you might sort them.

Can you think of some different criteria that you might use instead? Pause your video there, and have a go at that for me.

Okay, let's move on to have a look at another question now.

What is the fewest number of faces a polyhedron can have? I will just remind you, that a polyhedron is a 3D shape that only has flat faces.

So what's the fewest number of faces a polyhedron can have? Consider the 3D shapes you know, which of the 3D shapes you know has the fewest number of faces that is a polyhedron.

Pause your video there and have a think for me.

Okay, let's have a look together.

So the 3D shape that has the fewest number of faces, that is a polyhedron is a triangular base pyramid or a tetrahedron.

It has two different names.

So here is my triangular base pyramid, it has 1, 2, 3, 4 faces, and this is the smallest number of faces a polyhedron can have.

If it was to have three faces or less, it must have a curved side.

This is the smallest number of faces that a polyhedron can have.

Did you get the same answer as me? Okay, we're going to have a think about prisms now.

On screen there are five different shapes for you to look at and I would like you to identify which ones of them are prisms. Now, I will just tell you that a prism is a 3D shape that has the same identical face at either end.

And no matter where you cut that shape anywhere, it will always have an identical face at either end.

So pause your video and identify which of the shapes are prisms. Okay, let's have a look at our answers together.

So here we go, we can see that a sphere and a cone are not prisms because, here's my sphere.

If I was to cut that at any point, I would not have an identical face at either end.

And plus a sphere only has one face, so it can't have another identical face can it? Here is my cone, if I was to cut my cone in half, I wouldn't have the same face at either side again, so that's not a prism.

Let's have a look now at the shapes that are prisms. So the first shape I can see is a cylinder.

Here's my cylinder, it has a circular face at either end.

They're identical, and if I was to cut my cylinder, it would also have a circular face, no matter where I would cut it, so my cylinder is a prism.

Let's have a look at my cuboid now.

Looking at my cuboid, either end is a square face, they are identical to each other and if I were to cut it there, I would also have a square face, so that is also a prism.

And then finally, this shape here.

Now the clues in the name of this one, this is a pentagonal prism.

I know that because there is a pentagonal face at either end and they are identical, and if I were to cut this at any point, I would have another pentagonal face.

So these are the three that are prisms. Did you get the same answers? Okay, time for an independent task now.

You need to apply all of that learning.

For your independent task, what you need to do is look at the four different 3D shapes on screen and write a little description about each of them.

You need to name the shape, identify the number of faces, identify the number of edges, the number of vertices and the shapes of the faces.

You could say whether they are polyhedrons, whether they are prisms, you could think of objects that you know that are those shapes.

So using the criteria that is there, fill those in but also add any extra descriptions of your own.

Pause your video there and have a go at that for me.

Okay, let's go through the answers now.