Lesson Video: Vertices of 2D Shapes Mathematics • 1st Grade

Video Transcript

Vertices of 2D Shapes

In this video, we’re going to learn how to identify and count the vertices or corners of 2D shapes. This is Ethel. All through her life, she’s always wanted to fly a plane. So that’s what she’s learning to do. But she’s not flying just any old plane. Ethel wants to fly a jet plane. She wants to draw 2D shapes in the sky with colored smoke because Ethel says, “The most enjoyable thing about flying a jet plane is turning it so that it goes round corners.” Think she’s going to draw a triangle to start off with? Fly straight, turn, fly straight, turn, fly straight, and then turn to face the direction Ethel started. The 2D or flat shape that Ethel has drawn in the sky is a triangle.

We know this because Ethel flew straight three times. And we know that triangles have three sides. But did you notice how many times Ethel had to turn the plane? We said turn once, twice, three times. Ethel had to turn the plane whenever she started a new side of the triangle, in other words, where two sides of the triangle meet. We call these points vertices. This is just a mathematical word for corners.

The points where Ethel turned her plane are the corners of the triangle. Vertices is the plural. It’s the word we use when we’re talking about more than one corner. But let’s just make a note of the word we use when we are just talking about one corner. And that’s a vertex. So this is a vertex, but these are vertices. A triangle then has three vertices. It has three corners.

Looks like Ethel’s about to draw another 2D shape in the sky. This is an interesting shape. It’s a red arrow. Now, how many times did Ethel have to turn the plane? Let’s count the vertices. This red arrow has one, two, three, four corners or four vertices. These are the points where the sides of the shape meet. Let’s have a go at answering some questions now where we have to identify and count the vertices or corners of some 2D shapes.

Which of the given shapes has five vertices?

In this question, we’re given four different 2D shapes to look at. And the question asks us which of them has five vertices. Now we’re not going to be able to answer this question unless we know what the word vertices means. What are the vertices of a shape?

Well, we know one thing they’re not. They’re not the straight lines that make up a shape. These are the shape’s sides, not vertices. Vertices are the corners of a shape where two sides meet. Do you recognize our first shape? It’s a rectangle, isn’t it? How many vertices does this shape have? One, this is the corner where these two sides meet. Two, this is the corner where these two sides meet. Three, so you can see each of these vertices is a place where two sides meet. And then finally, there’s one more corner at the top.

Our rectangle has four corners. Using our special word for corners, we could say it has four vertices, so it’s not the shape we’re looking for. What about the next shape? Do you recognize this one? It’s a triangle, isn’t it? How many vertices does a triangle have? We can see one, two, three vertices. The triangle isn’t the shape we’re looking for either. The next shape is an interesting one. Let’s see whether this has five corners. One, two, this is an interesting one. It doesn’t stick out like all the other corners, does it? But remember, a vertex is the corner of a shape where two sides meet. And this is a point where two sides meet.

Just because it’s not sticking out doesn’t mean it’s not a corner. Three, four, five, six. This shape has one too many vertices. It has six vertices, not five. It looks like our last shape must be the right answer. Let’s count to see whether it has five corners. One, two, three, four, five. This shape has five vertices. We know that the vertices of a shape are its corners. And so the correct shape is the one that has five corners. It’s this shape.

Do the two given shapes have the same number of vertices?

We’re given a pair of 2D shapes to look at here. They look quite different, don’t they? And our question asks us to compare them. We need to decide whether there’s something similar about our shapes. Do they have the same number of vertices? We know that vertices is a mathematical word that’s used to describe the corners of a 2D shape. So we could replace the word vertices for corners in the question. Do the two shapes have the same number of corners? There’s only one way to find out. Let’s count them. Let’s put a counter on each of the corners of the first shape so we know which ones we’ve counted.

We’ll start with this corner at the top here. One, two, three, four, five, six. Our first shape has six corners or vertices. Now, let’s compare this with our second shape. Does this shape have six vertices as well? Let’s count them. One, two, three, four, five, six. Although our two shapes do look different, they both have the same number of vertices. Just goes to show, doesn’t it? Just because two shapes have the same number of vertices doesn’t mean they have to look exactly the same, does it? So, in answer to our question, do the two given shapes have the same number of vertices, we can say yes.

Leah builds a triangle out of plastic straws and blobs of clay. How many blobs of clay will she need to build a square?

We often think about drawing 2D shapes, don’t we? But this question is about building them. The 2D shape that we’re told Leah’s built is a triangle. And we’re told that she’s done this using plastic straws and blobs of clay. Can you see them in the picture? The plastic straws make up the sides of the shape. And because we know triangles have three sides, that’s why Leah’s used three plastic straws. Now, if the plastic straws are the sides of the triangle, what are the blobs of clay?

If you look carefully, we can see that Leah’s used a blob of clay to join two sides together. She’s used one at each point where two sides meet. And we call the points where two sides meet in a 2D shape its corners or vertices. Leah’s used a blob of clay in each of the three corners of a triangle.

The question asks us, how many blobs of clay will she need to build a square? As we’ve just said, Leah uses a blob of clay at each point where two sides meet, each corner of the shape. So we just need to count. How many corners or vertices does a square have? One, two, three, four. A square has four vertices. And because of this, we know that Leah is going to need four blobs of clay to build a square. We used our knowledge of 2D shapes to work out how many vertices a square has. The number of blobs of clay that Leah will need to build a square is four.

So what have we learned in this video? We have learned to identify and count the vertices of 2D shapes.