Lesson video

Hello everybody.

My name is Mrs. Johnson.

I am so excited to be here today to help you with some of your maths learning.

I hope you are ready to work hard and have lots of fun.

Let's see what we're going to be learning about today.

This lesson is called "Recognise and Sort Polygons." It comes from the unit, "Shape." Discuss and compare 2D and 3D shapes.

By the end of this lesson, you will be able to explain what a polygon is and sort polygons in different ways.

There are 4 key words in this lesson that we are going to practise now.

I will say them first and then it will be your turn.

Ready? My turn: Polygon.

Your turn.

My turn: 2D.

Your turn.

My turn: Two-dimensional.

Your turn.

My turn: Sides.

Your turn.

My turn: Vertices.

Your turn.

Well done! Did you notice that on one of our keywords, there are two different ways to say it? You can say 2D or you can say two-dimensional.

2D is a shorter way of saying two-dimensional.

There are going to be two parts to this lesson.

To begin with, you are going to find out what is a polygon and then in a little while, you are going to learn about how you can sort polygons.

Let's start by learning about what is a polygon.

There is one friend in this lesson today.

Her name is Sam and she's going to come and help us.

Listen carefully to the things that Sam has to tell you because they are really useful.

Sam has cut out some different 2D shapes from card.

Sam says, "I am going to show you some of the shapes." That's our polygons.

Let's have a look.

Wow, look at some of Sam's polygons.

I wonder if you notice anything about these polygons? Is there anything that they've got that is always the same? Sam is asking you an important question.

"What do you think a polygon is?" You know that all of these shapes are polygons.

What could a polygon be? That's a really good question that Sam has asked, isn't it? Let's have a look at that now.

A polygon is a 2D shape with straight sides.

You can see, can't you, that all of these shapes have straight sides.

There are no curves.

A polygon needs to have at least 3 sides.

All the sides must be straight and must join at vertices.

Let's have a look at what those things mean.

The sides must be straight.

You can see here, can't you? That these shapes all have straight sides.

The sides must join active vertices.

This is a vertex and this is a vertex and this is a vertex.

These are vertices.

It is the point where two of the sides join.

Let's check if you know the important things that a polygon needs to have.

Can you think of a way that you could complete Sam's sentence? This shape is a polygon because, hmm.

Pause the video and have a think.

How could you complete this sentence? Well done for thinking carefully about that.

Let's have a look at how you could have finished that sentence.

You might have said, "This shape is a polygon because it has straight sides." You also could have said this shape is a polygon because all the sides join at vertices.

Well done, if you remembered that a polygon needs to have straight sides and the sides need to join at vertices.

Sam is sorting some shapes now.

Only one of these shapes is a polygon.

Which one do you think it could be? I bet Sam knows, let's have a look.

Sam says this one is a polygon and this one is not.

I wonder why.

What do you think? Let's see what Sam says.

Sam says this is not a polygon because it is a 3D shape.

A polygon is a 2D shape.

Sam has remembered a polygon needs to be a 2D shape, which means a flat shape.

If a shape is 3D, like this cube is here, then it cannot be a polygon.

Sam says, only one of these shapes is a polygon.

Which one do you think could be the polygon this time? Let's see.

This shape is a polygon, this one is not.

I wonder why this shape is not a polygon.

Let's see what Sam thinks.

You can see if you agree.

Sam says, "This is not a polygon because it has curved lines." A polygon only has straight sides.

Only one of these shapes is a polygon.

Which one could it be this time? Let's have a look.

This shape is a polygon.

This shape is not a polygon.

Why could this shape not be a polygon? Let's see if you agree with Sam this time.

Sam says, "This is not a polygon because the straight sides do not meet at the vertices." If you look carefully at the shape that is not a polygon, you can see that it has curved lines.

Vertices are where two straight sides join to make a corner.

They cannot have a curved line, so the first shape is not a polygon, but the second shape is.

Only one of these shapes is a polygon.

Which one do you think could be a polygon this time? This shape is a polygon, and this is not.

Why could this one not be a polygon? Let's see what Sam thinks.

Sam says, "This is not a polygon because it is not a 2D shape." It has a gap and the gap means that it is not a 2D shape, because it's not a closed shape.

So if it's not a 2D shape, it cannot be a polygon.

Well done if you were thinking about that, too.

Let's check if you can explain why a shape is not a polygon.

Look carefully at this shape.

How could you complete Sam's sentence? Pause the video and have a think.

You could say this is not a polygon because it does not have straight sides, or you could say this is not a polygon because it has curved lines.

In a polygon, all the sides need to be straight.

How could you complete some sentence about this shape? This is not a polygon because.

Hmm, pause the video and have a think.

This time you could say this is not a polygon because it is not a two-dimensional shape.

This is a 3-dimensional shape, isn't it? This is a cylinder.

If it is a 3D shape, it is not a polygon.

Now it's time for you to practise to see if you can recognise which shapes are polygons and which shapes are not.

You can see that there are some shapes that you need to sort into sets.

The first set is called, "polygon," and the second set is called, "Not a polygon." Sam says, "Remember that a polygon is a 2D shape with only straight sides." I think Sam is helping you there to make sure that you sort each shape into the correct set.

You are going to pause the video and go and sort out those shapes now.

Off you go.

Let's see if you have sorted them into the correct set.

A is not a polygon because it has a curved line.

B is a polygon, all the sides are straight and it is a 2D shape.

C is not a polygon.

It's not a 2D shape because it has a gap.

D is not a polygon because it has curved lines at the corners.

The sides don't join to make vertices.

E is a polygon.

All the sides are straight and the sides meet at vertices.

F is not a polygon because it has curved lines.

G is a polygon.

All the sides are straight and they meet at vertices.

H is a polygon because all the sides are straight and they meet at vertices.

I is not a polygon because it is not a 2D shape, is it? It is a 3-dimensional shape.

Did you notice that all the shapes in the polygon sets have 3 or more straight sides? They are two-dimensional shapes whose sides all meet vertices.

Well done for thinking really carefully about why a shape might be a polygon or why it might not be a polygon.

Good job.

Now it is time to have a look at the second part of this lesson.

Now we are going to be thinking about this question.

"How can I sort polygons?" I wonder, have you got any ideas about how we might be able to sort polygons? Let's have a look.

Sam counts the sides that each polygon has.

She says, "I will mark each side as I count so that I know I have counted each side once." This is going to help Sam count them carefully so that she doesn't make any mistakes.

1, 2, 3, 4.

1, 2, 3, 4.

1, 2, 3, 4.

Oh, do you notice something about Sam's counting of the sides? Yes, well done.

Each of these polygons has 4 sides.

The polygons don't all look the same, but they do all have 4 sides.

Now Sam counts the sides of some different polygons.

She's going to mark the sides again as she counts to make sure that she doesn't make any mistakes with her counting.

Let's have a look.

1, 2, 3, 4, 5.

This one has 5 sides.

1, 2, 3, 4, 5, 6, 7, 8.

This polygon has eight sides.

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12.

This polygon has 12 sides.

It is really helpful to do what Sam has done and mark each side as you count to help you to count accurately so that you don't make a mistake and it makes sure that you count every side once.

Let's check if you can count the sides of some polygons accurately.

Which polygons have 6 sides? Pause the video and count the sides really carefully so that you can see which polygons have 6 sides.

Off you go.

Well done.

You were counting really carefully.

Let's have a look.

The first polygon has 1, 2, 3.

3 sides, not 6 sides.

The next polygon has 1, 2, 3, 4, 5, 6.

It does have 6 sides.

The next one, 1, 2, 3, 4, 5, 6, 7.

Not 6 sides.

The next polygon has 1, 2, 3, 4, 5 sides, not 6.

The next polygon has 1, 2, 3, 4, 5 sides, not 6.

And the last polygon has 1, 2, 3, 4, 5, 6 sides.

Yes, this one does have 6 sides.

Well done if you were able to count the sides of those polygons accurately so that you could find which ones had 6 sides.

Sam knows how many sides each polygon has.

She could sort them into sets.

Look at the names of her sets this time.

"Does not only have 4 sides," "Has only 4 sides." Let's watch her sort these shapes into these two sets.

This one has only 4 sides.

This one has only 4 sides and this one has only 4 sides.

They have only 4 sides because they don't have more than 4 and they don't have less than 4.

They have only 4.

The next polygon does not only have 4 sides.

It goes in this set because if you count them, it has 5 sides.

So it does not only have 4.

The next polygon goes in the "Does not have only 4 sides." This one had eight sides and the last polygon does not only have 4 sides.

This one had 12, didn't it? Sam can sort her polygons into sets by looking at how many sides they have.

She could sort them by the number of sides in a different way.

Let's look at the name of her sets this time.

6 or more sides, fewer than 6 sides.

Let's see where the polygons end up this time.

Fewer than 6 sides, fewer than 6 sides, fewer than 6 sides.

So far these 3 shapes have ended up in the same set as last time, haven't they? The next shape has 5 sides, so it will go in the fewer than 6 sides set.

The next shape had eight sides, that goes in 6 or more sides.

And the last shape has 12 sides.

That goes in the 6 or more sides set.

Let's check if you can sort polygons into sets.

This time, your sets are called, "Fewer than 5 sides," "5 or more sides." Have a look at these polygons and see if you can decide which set each polygon belongs in.

Pause the video and have a go at that now.

Well done.

You were counting the sides really carefully.

Let's see if you have sorted each polygon into the correct set.

This one has 5 or more sides.

It has 6.

This one has fewer than 5 sides because it has 3 sides.

This one has 5 or more sides.

It has 5, doesn't it? The next one has fewer than 5 sides because it has 4 sides.

This shape has 5 or more sides.

It has 7, and the last shape has 5 or more sides because it has 6 sides.

Well done if you were able to count the sides and sort those polygons into the correct sets.

Good job so far.

Sam has been counting the sides of the polygons, but Sam could also count the vertices that each polygon has.

Sam says, "I will mark each vertex as I count so that I know I have counted each vertex once." Oh, this is really similar to when she was counting the sides, isn't it? Let's watch Sam count the vertices.

1, 2, 3, 4.

You can see that she's drawn a mark on each vertex so she knows when she's counted them.

1, 2, 3, 4.

1, 2, 3, 4.

Each of these polygons has 4 vertices.

Sam counts the vertices of some different polygons.

1, 2, 3, 4, 5.

1, 2, 3.

1, 2, 3, 4, 5, 6.

Sam drew a mark on each vertex as she counted them to make sure that she could count the vertices accurately.

That is a really helpful way that you can count the vertices without making a mistake.

Let's check if you can count vertices.

Have a think about this.

Is this true or false? This polygon has 5 vertices.

Pause the video and have a think.

Well done for thinking carefully about that.

Let's have a look.

How many vertices does this polygon have? Is it 5 or is it a different number? Let's mark the vertices to check.

1, 2, 3, 4, 5, 6, 7, 8, 9, 10.

This is false! When you count each vertex, you can see this polygon has 10 vertices, not 5.

The person who counted 5 vertices must have missed some out mustn't they, they didn't count all the vertices.

Perhaps they needed to use Sam's method of marking a line on each vertex to make sure that she counts them accurately.

Now that Sam knows how many vertices each polygon has, she can sort them into sets.

This time her sets are called, "Has 4 or fewer vertices," "Has more than 4 vertices." Let's watch how Sam can sort her polygons this time.

This one has 4 or fewer vertices.

It has 4, doesn't it? This one has 4 or fewer vertices because it has 4.

And this shape has 4 or fewer vertices because it has 4 as well.

The next one has more than 4 vertices.

This one has 4 or fewer vertices.

This shape has 3 vertices, doesn't it? So it belongs in the 4 or fewer vertices set and the last shape has more than 4 vertices.

It has 6 vertices.

Let's check if you know how to sort shapes by the number of vertices.

Have a look at these polygons that have been sorted into sets.

Some of them are in the wrong place.

I wonder if you can look really carefully.

The first set is called, "Has 5 or fewer vertices." And the second set is called, "Has more than 5 vertices." Which polygons might be in the wrong place? Pause the video and have a really good look.

Oh, well done.

You were checking each polygon really carefully, weren't you? One of the polygons you might have noticed in the wrong set is F.

It has 6 vertices, but it is in the 5 or fewer vertices sets, so it needs to move into the set that is called, "More than 5 vertices." The other polygon you might have noticed that is in the wrong place is D.

If you count the vertices on D, you will see that it has 5 vertices, so it should be in the 5 or fewer vertices set.

Well done.

If you noticed that both of those were in the wrong place.

Now it's time for you to go and have a practise at sorting polygons into sets.

I would like you to have a look at these polygons.

Look carefully at how they have been sorted.

Then you need to write a label for each set of polygons.

You need to decide what you would like to call each set.

You could sort by the number of sides or the number of vertices.

Sam's given us a little clue there, hasn't she? Thank you, Sam.

Once you've decided on what you are going to call each set, you are going to sort these polygons into the correct set so you can draw them, or you can write the letters A, B, C, and D to show where you would put each polygon.

Finally, you are going to draw some more polygons in each set, so you've got to think carefully about what you have called your set and draw some more shapes that would belong in that set.

I know you've been thinking so carefully about sides and vertices and polygons in this lesson.

You are going to do an amazing job at this work.

Are you ready? Off you go.

Well done, I knew you were going to try really hard at that work and do an excellent job.

Let's have a look at how you could have sorted these polygons.

You could have decided to call one set 4 or fewer sides and one set more than 4 sides.

You should have noticed that the shapes in the first set have 3 sides or 4 sides.

The shapes in the second set have 6 sides.

If you chose these names for your sets, this is how you would sort the polygons.

A has more than 4 sides.

B has more than 4 sides.

C has 4 or fewer sides, and D has more than 4 sides.

Maybe you didn't choose these names for your sets.

Maybe you didn't choose to think about the number of sides at all.

You might have thought about the number of vertices.

Let's have a look at another example of how you could have sorted these polygons.

You could have called your sets, "Does not have 6 vertices," and "Has 6 vertices." If you chose those names for your set, Some of these polygons would need to move, wouldn't they? They're not sorted correctly anymore.

Let's have a look at how we would sort them now.

B does not have 6 vertices, so it needs to move into the other set.

D does not have 6 vertices, so that needs to move into the other set.

Now they have been sorted correctly.

You might have drawn some more polygons in each set like this.

In the "Does not have 6 vertices" set, you needed to draw some polygons, so shapes with straight sides that do not have 6 vertices.

Maybe you drew something like this or you could have drawn a rectangle like this.

In the "Has 6 vertices set," this is tricky.

You need to draw some shapes that have 6 vertices and they need to have straight sides because if they don't have straight sides, they are not polygons.

You could have drawn something like this.

This one has 6 vertices.

Or maybe you might have drawn a shape like this.

Well done for thinking really carefully about the name of each set, whether you are looking at sides or vertices and how you can sort those polygons into the correct sets.

You've done a really good job, well done.

Now that you are at the end of the lesson, you know that a polygon is a two-dimensional shape, which has 3 or more straight sides that join vertices.

You can explain why a shape is a polygon or why it is not a polygon.

You can count the sides and the vertices of a polygon accurately by marking them as you count to help you to not make a mistake.

You have worked really hard in this lesson today and done some excellent thinking about polygons.

Well done.

I hope that I will see you again soon for some more maths learning.

Bye, everybody!.