Lesson Video: Sides of 2D Shapes | Nagwa Lesson Video: Sides of 2D Shapes | Nagwa

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

In this video, we will learn how to identify and count the sides of 2D shapes.

09:37

### Video Transcript

Sides of 2D Shapes

In this video, we’re going to learn how to identify and count the sides of 2D shapes.

This is Larry. He’s been hired to paint the white lines on a sports field. But there’s one thing about Larry. Once he gets going, he can only paint straight lines. This leads to him painting some very interesting 2D shapes. What happens if he paints a square? He paints one, two, three, four straight lines. And you know we can call these straight lines the sides of the shape. A square is made up of one, two, three, four straight sides. And one thing we know about the sides of a square is that they’re all the same length.

I think Larry might be about to paint another shape. How many sides are there on this shape? We could find out how many this time by placing a counter on each side. This shape is made up of one, two, three straight sides. Can you remember the name of the shape that Larry’s painted? It’s a triangle. Triangles are shapes that have three straight sides.

Oh, it looks like Larry’s really got carried away this time. He’s painted a shape just like the first letter of his name. How many straight lines did Larry need to paint to paint this shape? To make sure we count each line only once, let’s trace over them in different colors. One, two, three, four, five, six. Six straight lines means six sides. We could say that Larry has painted a six-sided shape.

So, how well do you think you can find and count the sides of 2D shapes? Shall we have a practice? Let’s try some questions where we have to use this skill.

Which of the given shapes has four sides?

We’re shown a picture here of four different 2D or flat shapes. We can see that each of the shapes is made up of a number of straight lines. We call these straight lines the sides of the shape. Now, each of these shapes has a different number of sides. But we’re asked to find the shape that has four sides. Let’s count the sides on each shape to find out which one it is.

We could put a counter on each side to show that we’ve counted it. The first shape has one, two, three, four, five sides. This isn’t the shape we’re looking for. We’re looking for a four-sided shape. Let’s try the next one. Do you recognize this next shape? It’s a triangle. And the one thing that we can say about triangles is that we can draw them by joining up three straight lines. They have three sides. So, this isn’t our shape either.

Our third shape has one, two, three, four sides. It looks like this is the shape we were looking for. And if we just check the final shape, we can see that this has six sides. So, we’ve identified the shape that has four sides. And you know what the name of that shape is? It’s a square. Each of the four sides is the same length. And if you think that this doesn’t look like the usual way you draw a square, turn your head slightly. This is just a square that’s been turned a bit. That’s all. This is the shape that has four sides.

True or false? Shape A and shape B have the same number of sides.

Underneath the question, we can see pictures of two shapes. And both of these shapes have been made from straight lines. We call these straight lines the sides of the shape. Our question is made up of a statement which tells us that shape A and shape B have the same number of sides. In other words, these 2D shapes are made up of the same number of straight lines.

But this statement might not be correct. We need to decide whether it’s true or false. To make sure that we count all the sides of a shape and also that we only count each one once, let’s trace over them as we count them. Let’s start from here on shape A, which is made up of one, two, three, four sides. We can say shape A is a four-sided shape.

Now, let’s trace over the sides of shape B. We’ll start from this bottom corner. There are one, two, three, four sides again. Although shape 𝐵 is a different sort of shape to shape A, it’s still a shape with four sides. We’ve counted the number of sides that make up each shape. And we can see that they’re both the same. The statement in the question is true.

Jacob has built a square with four sticks. How many sticks does he need to build a triangle?

You know, we can draw 2D shapes. But, in this question, Jacob has built one. We’re told that Jacob has used four sticks to build his shape. They look a bit like ice lolly sticks, don’t they? And the question tells us that the name of Jacob’s shape is a square. And in the picture, we can see the four sticks that he’s used. One, two, three, four. Why has Jacob used four sticks to build his square? Why hasn’t he used two or three or five?

Well, we know the reason why Jacob has used four sticks is because squares have four straight sides. And each side is the same length. So, it’s very easy to do when all your lollipop sticks are the same length. Squares have four sides.

Now, our question goes on to ask us, how many sticks does Jacob need to build a triangle? And to answer the question, we’re going to have to think how many straight sides does a triangle have. We know that to draw a triangle, we need to draw one, two, three straight lines. Triangles are shapes that have three sides. And so, Jacob can build his triangle out of one, two, three sticks.

Although it didn’t mention the word in it, this question was all about the sides of 2D shapes. We know that squares have four sides. And that’s why Jacob could build his square using four sticks. And we also know that triangles have three sides. And that’s why the number of sticks that Jacob’s going to need to build his triangle is three.

So, what have we learned in this video? Firstly, we’ve learned that the straight lines that form a shape are its sides. We’ve also learned how to identify and count the sides of 2D shapes.