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

Let's have a look at what we are going to be learning about today.

Today's lesson is called, "Explore, Discuss, and Identify Shapes That Are and Are Not Triangles." It comes from the unit, "Recognise, Compose, Decompose, and Manipulate 2D and 3D Shapes." In this lesson, you are going to learn lots more about triangles.

By the end of the lesson, you will be able to say if a shape is a triangle or not, and you will be able to explain why.

You might want to think about what you already know about triangles.

Maybe you could have a look around you and see if you can spot any triangles, to help you remember what a triangle looks like.

That might really help you for the rest of this lesson.

There are some key words that you are going to use in this lesson today, and I'd like you to practise saying them after me.

I'll have my turn and then it will be your turn.

Ready? My turn.

Triangle.

Your turn.

My turn.

Sides.

Your turn.

My turn.

Vertices.

Your turn.

My turn.

Straight.

Your turn.

Well done.

Listen for all of those words in this lesson, and when you are doing your work, try to use these words as much as you can.

They are really important for the work that we are doing about triangles today.

There are going to be two parts to this lesson.

To begin with, you are going to learn how you can describe shapes, and then in a little while, you are going to learn how you can sort shapes.

Let's start by learning about describing shapes.

Look out for these two people in our lesson today, Laura and Andeep.

They are going to come along throughout the lesson and help you by giving you important information about triangles.

Watch out for them throughout the lesson.

Okay, let's start our learning about triangles.

Laura has cut out some different shapes from a piece of card.

We can see all the shapes that Laura has here.

She says, "I think that one shape looks like a slice of pizza." Andeep says that he thinks one shape looks like a wave.

What do you think? Can you see any that remind you of something else? When you look carefully at different shapes, sometimes some of them might remind you of something else that you've seen before.

Sometimes they might be a similar shape.

I wonder if you can work out which shape Andeep is describing now.

He says, "I think that one shape looks like a sharp tooth." Do you think it's A, B, or C? I hope everybody said B.

B does look like a sharp tooth, maybe from a shark, or maybe it looks a bit like a fang from a snake's mouth.

Something sharp and pointy.

What about this one? Laura says, "I think that one shape looks like a windmill." Do you think she might be talking about A, B, or C? Laura is describing A.

She thinks it looks a bit like a windmill.

I wonder what you think.

Do you think it looks like a windmill? Or does that shape remind you of something else that you've seen before, maybe? You can describe shapes using words that you already know.

For example, Laura says, "I can see a wide shape." Andeep says, "I can see a curved shape." I wonder what you would say.

Look at what you can see.

How might you describe this shape? Pause the video if you would like a little bit longer to think or to talk to somebody about this.

Good thinking, everybody.

There are lots of different words that you might use to describe this.

You could say that this is a narrow shape, or you might say that this is a long shape.

I'm sure there are lots of other words that you thought of that you could use too.

Well done.

When you do describe a shape, you do have to look carefully at it, and think really carefully about what you can see.

Sometimes, it can also help to imagine holding the shape in your hands, and thinking about what it might feel like if you could hold it.

Laura says, "If I could hold this shape in my hands, the corners would feel smooth." Andeep says, "If I could hold this shape in my hands, the corners would feel sharp and pointy." Can you imagine holding those shapes in your hands? I bet that the shape Andeep is talking about would feel very sharp and pointy, and the shape that Laura is talking about wouldn't, you can see, can't you, that the corners on Laura's shape are much more smooth because they are curved? They don't look pointy like the corners on Andeep's shape.

Which shape do you think Laura is talking about now? She says, "If I could hold this shape in my hands, it would feel curved." Is she talking about A, B, or C? Laura is describing C.

C is the only shape that would feel curved all the way around.

If you were thinking about B, B does have a curve on it, but it also has two lines that are straight, and parts of that shape would feel very pointy.

It wouldn't feel curved all the way around.

There's only one small curve on it.

The shape on C would feel curved all the way around.

Andeep says, "If I imagine holding this shape, I would only be able to feel one sharp corner." Do you think that is A, B, or C? Andeep is describing shape A.

If you look really carefully, A only has one sharp corner.

Because the corners at the top of the shape are curved, they wouldn't feel sharp.

Shape B and shape C, all the corners look sharp on those shapes.

They look sharp and pointy, don't they? They are not smooth or curved.

If Andeep says, "I would only be able to feel one sharp corner," he must be talking about shape A.

These shapes that you can see here, are all triangles.

Have a look at them.

Does this help you to remember anything that you might have learned before, about triangles? Laura says that triangles have only three straight sides.

Andeep says triangles have only three vertices.

Let's have a little bit of a look in a bit more detail about what Laura and Andeep have said.

We're going to count the sides of these triangles.

You might have done something like this before, so count along with me and let's help everybody remember how to count the sides on a triangle.

Ready? One, two, three.

Three sides.

One, two, three.

Three sides.

One, two, three.

Three sides.

Triangles always have three straight sides.

There are no curved lines here, triangles always have straight sides.

Sometimes, shapes can look really similar and you have to look really carefully to find out how they are different.

Have a look at these two shapes.

When you first look at them, they look the same, but if you keep looking really closely and really carefully, you might notice what Andeep has noticed, that the first shape looks different in one of the corners.

Laura says, "Let's count the sides to check." Are you ready to count the sides with me? Let's go.

One, two, three, four.

Four sides.

One, two, three.

Three sides.

When we count the sides, we can see that these shapes are different.

One shape has four sides and one shape has three sides.

Counting the sides helped us to check if these shapes were the same or if these shapes were different.

Can you spot which shape has only three straight sides? Do you think it's A, B, or C? The shape with three straight sides, only three straight sides, is C.

A has six straight sides, and B has four straight sides.

You are looking for C because that is the shape that has only three straight sides.

Well done if you found C.

Let's see if you can find another shape.

You are looking for the shape that has only three straight sides.

Could it be A, B, or C? This time, it's B.

A has more than three straight sides, doesn't it? And C, you have to look very carefully at, because when you first look, you might think that it has three sides, but when you check carefully, C does not have only three straight sides because some of them are curved lines.

The shape that you are looking for is B.

Now that we've looked at sides, let's have a think about vertices.

Can you count the vertices of these triangles with me? Ready? One, two, three.

Three vertices.

One, two, three.

Three vertices.

One, two, three.

Three vertices.

Triangles always have three vertices.

Let's learn a little bit more about vertices and how to find them in a triangle.

In 2D shapes, a vertex is a point where two straight sides meet to make a corner.

If you see a corner that is made of two straight sides, that is a vertex, and when you have more than one, they are called vertices.

This shape has one, two, three, three vertices, because all the sides are straight.

If the lines that meet are curved, it is not a vertex.

This shape here has zero vertices because the lines are curved, there are no straight sides, that means there are no vertices.

Vertices often look sharp and pointy.

If a corner looks curved, or round, or smooth, it is not a vertex.

Vertices must be made with straight sides.

This shape here, only has one vertex, because the two corners at the top of the shape are curved and round, they are not made from straight sides joining to make a corner, so they are not vertices.

This shape only has one vertex.

Let's see if you can find the shape that has three vertices.

Do you think it could be A, B, or C? The shape that has three vertices is A, it cannot be B and it cannot be C, because we need to remember that the sides meeting at a vertex are always straight, not curved.

Can you see that B and C both have curved lines? So they do not have three vertices.

We were looking for shape A.

You've got one more try, let's see if you can find the right shape again.

You are looking for a shape that has only three vertices.

Could it be A, or B, or C? The shape that you are looking for that has only three vertices is C.

A has some curved lines, and we know that if the lines are curved, it doesn't make vertices.

B has more than three, you were looking for the shape that has only three, so the shape you are looking for is C.

Now it is time for you to go and do a little piece of work.

You are going to have a look at all the shapes on your sheet, and you are going to count the sides of each shape.

Then you can choose a colour, and colour in the shapes that have only three straight sides.

Do a quick check.

Do all the shapes that you've coloured in also have three vertices? Once you've done your colouring and you've checked the number of vertices, have a think about this, can you name the shape that you've been asked to find? Look at all the shapes that you've coloured in.

Can you remember the name of that shape? Then, can you draw that shape by yourself? Go and have a really good try.

Off you go.

Well done, everybody.

You tried really hard to count the sides of all of those different shapes, and then look carefully at the vertices too.

These are all the shapes that have three straight sides.

These are the shapes that you should have coloured in.

Did you notice that all of these shapes have three vertices too? If they have three straight sides, they also have three vertices.

Did anybody have a go at drawing your own? And could anybody remember what these shapes are called? I'm sure you could.

Let's have a look.

These are all triangles.

This is what Andeep's drawing looked like.

He drew a triangle, and he made sure that it had three straight sides and three vertices.

Well done if you tried hard to draw your own triangle with three straight sides and three vertices.

You are going to learn a little bit more about sorting shapes, and then you are going to have a go at sorting some shapes too.

Andeep is going to sort these shapes into two sets, called triangle and not a triangle.

Let's watch how he sorts them.

I wonder what he was looking for when he decided where each shape was going to go.

Andeep says, "I know that a triangle has only three sides." The shapes in the not a triangle set have more than three sides, so Andeep must have been counting the sides of each shape.

If he found it had three straight sides, he put it in the triangle set.

If he found it had more than three sides, he put it in the not a triangle set.

Oh, now he's got some more things to sort.

This time, Laura drew these for Andeep to sort into sets.

Let's see what happens when he sorts them.

Watch carefully where each one goes.

I wonder what Andeep noticed about the things that Laura drew for him.

He remembered that a triangle has only three sides.

If we look at the shapes that Andeep has put into the triangle set, we can see, can't we, that they all have three straight sides? I wonder what he noticed about the things that he's put in the not a triangle set.

The drawings in the not a triangle set have less than three sides.

They look a bit strange, don't they? They don't really look like shapes, because they look a bit open.

They are not triangles because they are not a closed shape.

It's almost like Laura started drawing a triangle, but she didn't quite finish it because she forgot to draw the last side.

Because these drawings have been left open, they are not a closed shape, they cannot be triangles, so they belong in the not a triangle set.

Andeep has found some more shapes to sort.

Let's see what happens this time.

Watch carefully.

Where is each shape going to go? What do you think Andeep has noticed this time? We know a triangle has three straight sides, what do the shapes in the not a triangle set have? Well done if you've noticed they have curved lines, they cannot be triangles because a triangle has to have three straight sides.

If you spot a shape with a curved line, it cannot be a triangle.

I wonder if you can do some sorting.

Have a look at these shapes.

Which ones belong in the triangle set and which ones belong in the not a triangle set? Pause the video and have a go at sorting these into sets.

Let's have a look and see how you've got on.

This is how you should have sorted the shapes.

The first one is not a triangle because if you look really carefully, there are actually four straight sides, not three.

The second shape is a triangle, it has three straight sides and three vertices.

The next shape is not a triangle because it has curved lines.

The next shape is a triangle.

And the last shape is definitely not a triangle, because it has more than three straight sides.

Andeep is reminding us, "A triangle always has only three straight sides and three vertices." If it doesn't meet those rules, it cannot go in the triangle set.

Now have a look at these shapes, Laura has already sorted these shapes into her sets, triangle and not a triangle, but she's realised that she made a mistake.

We going to have a look at it together.

Laura has remembered that she forgot to look carefully at the vertices.

The sides that meet at a vertex should always be straight.

If the lines look curved, it is not a vertex.

Can you spot which shape she might have put in the wrong place? Yes, I think you've noticed.

It's this one, isn't it? The corners are too round.

They are not vertices.

This is not a triangle, so it needs to move into the not a triangle set.

To be able to sort shapes into these two sets, you have to check two very important things.

First, you have to check, are the sides straight? And then you have to check, does it only have three straight sides and three vertices? If you check both of those things, you will be able to sort your shapes into triangle and not a triangle.

Let's watch how Laura and Andeep check those things when they are sorting their shapes.

Here's the first shape.

Laura's going to ask the important questions and Andeep is going to answer.

"Are the sides straight?" Andeep is checking.

You can help him check.

He says yes.

Now it's time for the second important question, "Does it have only three straight sides and three vertices?" Andeep is thinking.

You can help him answer.

He says, "Yes, my shape is a triangle." It goes in the triangle set, because the answer to both of those questions was yes, it must be a triangle.

What's going to happen with this shape? Let's look at Laura's questions again, "Are the sides straight?" Andeep his thinking.

No, they are not.

He can see some curved lines.

The second question, "Does it have only three straight sides and three vertices?" Andeep says, "No, my shape is not a triangle." So the answer to both questions was no, the shape definitely cannot be a triangle, can it? It goes in a not a triangle set.

They have one more shape.

Laura's first question, "Are the sides straight?" Andeep's just checking.

You can help him check.

He says, "Yes, all the sides are straight." What about the second important question? "Does it have only three straight sides and three vertices?" Andeep's just having a look.

See if you can count them for him and check.

Andeep says, "No." He can see it has more than three.

"My shape is not a triangle." It goes in the not a triangle set.

You are going to use Laura and Andeep's important questions that you can see at the bottom, to spot the mistakes in these sets of shapes that have been sorted.

Pause the video and see if you can find the shapes that have been put in the wrong set.

Let's have a look.

How many shapes have ended up in the wrong place? This one should not be in the triangle set.

This one should not be in the triangle set.

Do we think there's any more? You are right, there is another one.

This one has been put in the not a triangle set, but it's in the wrong place.

Let's have a think about why.

The first shape has curved lines.

Triangles cannot have curved lines, they must have three straight sides.

The second shape has four straight sides, not three.

A triangle must have three straight sides.

If it has four, it belongs in the not a triangle set.

And the last shape has three straight sides, that means it is a triangle and it belongs in the triangle set.

Well done if you noticed all of those mistakes in that sorting.

Now it's time for you to go and do a bit of sorting work on your own.

There are some shapes with this lesson that you can have printed out, or an adult might be able to cut some shapes out for you that you will be able to sort, and you are going to sort them into sets just like Laura and Andeep did.

You are going to sort them into triangle and not a triangle.

When you have finished sorting all of the shapes, using the same shapes that you've just sorted, you are going to choose one shape to match each sentence here.

The first sentence is, a shape that is a triangle, so you have to choose one shape that shows it is a triangle.

Then you choose one shape that is a bit like a triangle.

And finally, one shape that is nothing like a triangle.

Once you've made your choices, I would like you to tell a partner why you chose each shape for each sentence.

When you are talking to your partner, see if you can use the keywords from today's lesson, so I would like you to be using the words triangle, straight, sides, and vertices, when you talk to your partner and tell them why you chose each shape.

Off you go.

Let's have a look at how you might have sorted your shapes.

I bet you were looking really carefully and checking if it had three straight sides and three vertices.

If you did, if you checked those things carefully, this is how you would have sorted your shapes.

You would've found there are six shapes that are triangles, and all the rest belong in the not a triangle set.

Laura and Andeep were partners when they were choosing shapes to match their sentences.

Let's have a look at the shapes they chose and the reasons they gave.

You can see if they said anything that was similar to what you said when you were talking to your partner.

The first sentence was a shape that is a triangle.

Laura chose this one.

She said, "It is a triangle because it has only three sides and three vertices." Next, the sentence was a shape that is a bit like a triangle.

Andeep chose this one, and he said, "This one is a bit like a triangle because it looks like a triangle, but with one vertex cut off." So it looks like one of the corners is missing, doesn't it, and it's been cut off? The last sentence was a shape that is nothing like a triangle.

Laura chose this one.

She told Andeep that this shape is nothing like a triangle because there are no straight sides, it only has curved lines, and Laura knows that a triangle has to have straight sides and no curved lines.

Well done if you worked hard like Laura and Andeep, and you were able to use the keywords to explain to your partner why you chose each shape.

Now that you are at the end of the lesson, you have learnt that triangles have only three straight sides and three vertices.

You've learnt more about vertices, and now you know that a vertex is only made when straight sides join in a corner.

You know that if the lines are curved, it is not a vertex.

You have learnt to sort shapes into sets, and you are able to explain why you have sorted them in that way.

You have done some very good thinking in this lesson, and some very good explaining too.

You have all worked very hard.

I hope that you will be back soon to do some more maths learning.

I hope I'll see you all again next time.

Bye, everybody.