# Lesson Video: Roll, Stack, and Slide Mathematics • Kindergarten

In this video, we will learn how to classify three-dimensional shapes based on their ability to roll, stack, and slide.

10:28

### Video Transcript

Roll, Stack, and Slide

In this video, we’re going to learn how to sort out 3D shapes based on whether we can roll them, whether we’re able to stack them, or whether the shapes will slide. Some shapes only do one of these things, some do two, and some even do all three.

Let’s begin by thinking about these three doing words: roll, stack, and slide. Now, we know when something rolls, it turns over again and again and again. Now, for a 3D shape to roll, it needs to have a curved surface. That’s what makes it roll. This bowling ball is a sphere. And one thing we know about spheres is that they have a curved surface all the way around. So when we let go of our bowling ball at the end of the alley, it’s going to start to roll. If a shape has a curved surface, it rolls.

Now, when something slides, it moves smoothly across a surface without turning over and over. There’s a word that rhymes with slide that means a very similar thing, glide. Now, for a 3D shape to slide, it needs to have a flat surface. This cuboid shape isn’t going to roll, but it will slide if we push it. This is because it has a flat surface. In fact, cuboids have lots of flat surfaces.

When we stack something, we put it on top of something else. For us to be able to stack a 3D shape, it needs to have a flat surface at the top and also at the bottom. This tin of beans is a cylinder. Although it has a curved surface all the way around, it has a flat surface at one end and another flat surface at the other. This means that we can stack cylinders. And that’s why when we go to the supermarket, we often see tins that are stacked up.

Now, we did say at the start of the video that some shapes can do all three. They can roll, they can slide, and they can be stacked. And cylinders are interesting because they’re one of these shapes. We already know that they can be stacked. If we put them standing up on their flat surface and push them, they’ll slide. But cylinders also have a curved surface too. And if we turn this cylinder on its side and push it, it’s going to roll. So a cylinder is a really good example of a shape that we can roll, stack, and slide.

Do you think you know enough now to be able to tell whether we can roll, stack, or slide a shape? Let’s try some questions and see.

Where does this shape belong? Can roll or cannot roll.

In this question, we can see a picture of a cylinder. We can tell it’s a cylinder because it has a curved surface all the way around. But there are two flat surfaces too, one at each end. Our question asks us, where does this shape belong? And we’re given two possible groups. Does it belong with the shapes that can roll? Or does it belong with the shapes that cannot roll?

We know when something rolls, it turns over and over. And we know that a 3D shape can roll if it has a curved surface. That’s why if we look at the shapes in the first group, they each have a curved surface. This is what helps them turn over and over as they roll along. If you look at the shapes in the second group, we can’t see any curved surfaces at all. That’s why they cannot roll.

So to help us decide where to put our cylinder, we could simply ask, does a cylinder have a curved surface? The answer is yes. A cylinder does have a curved surface all the way around. So if we turn our cylinder on its side, we can make it roll. Our shape belongs in the group of 3D shapes that can roll.

Which group does this shape belong to? Cannot slide or can slide.

In this question, we’re shown a picture of a 3D shape. If we look at it carefully, we can see that it has a curved surface all the way around. At one end, there’s a flat surface. And at the other end, it goes to a point. It’s a cone. We need to think carefully about whether cones can slide or not because we’re given two groups. And we need to decide which one to put our cone in. Shall we put it with the shapes that can slide? Or what about this sphere here which cannot slide?

We know that when something slides, it moves smoothly across a surface. It’s not the same as rolling over and over. And so we know that 3D shapes can slide only if they have a flat surface. That’s why this sphere is in the “cannot slide” group. It doesn’t have a flat surface at all. It’s completely curved all the way around. And when we push it, it rolls. But if we look at our two shapes in the “can slide” group, we can see that they both have flat surfaces. So by pushing them, we can make them slide across a tabletop.

Now, let’s look at our cone. Does it have a flat surface? Yes, it does. It’s on the bottom of this particular picture. So if we put our cone on the tabletop like this and push it, it’s going to slide. It has a flat surface. And so because our 3D shape has a flat surface, the group that it belongs to is the group of shapes that can slide.

Think about shapes that can roll, stack, and slide. One of these shapes can roll and slide. Which one? One of these shapes can slide and stack. Which one?

This question encourages us to think about whether shapes can roll, stack, and slide. And you know some shapes can do more than one of these things. The first part of the question asks us to find one of the shapes that can both roll and slide. And we’re given two shapes to look at. The green shape is a cube, and the red shape is a cone.

Now, which of these two shapes can do two things, roll and also slide? Now, for a 3D shape to slide along if we push it, it’s going to need to have a flat surface. But we can see that both of our shapes have at least one flat surface. So they’re both going to be able to slide. But for a 3D shape to roll, it’s going to need to turn over and over again. And for this, it’s going to need a curved surface. Which of our two shapes has a curved surface? It’s the cone. It has a flat surface and a curved surface. And if we stand it upon its flat surface, it will slide. But if we turn it onto its curved surface on the side, we can make it roll too.

In the second part of the question, we’re shown two more 3D shapes. The first shape is not a cuboid, but it might remind us of one. Looks a little bit like a cuboid, doesn’t it? And we know the name of our second shape. It’s a pyramid. And we’re told that one of these shapes can slide and also stack. Is it our unusual yellow shape or our purple pyramid?

Well, we already know that to slide a shape, it needs a flat surface. And both of these shapes do have a flat surface. If we put them on a tabletop and push them, they’d both slide. But which one could we stack on top of each other? Well, for us to be able to stack a 3D shape, it needs to have flat surfaces at either end. Our pyramid might have a flat surface at one end, but at the other end there’s a point. Can you imagine trying to balance one pyramid on top of another? We can’t stack pyramids.

But if we look carefully at our first shape, we can see that it does have flat surfaces opposite each other. Because it’s such an unusual shape, it might make a bit of a wonky tower, but we can still stack it. The shape that can both roll and slide is the red cone, and the shape that can both slide and also stack is the yellow shape.

So what do we learn in this video? We’ve learned how to sort 3D shapes based on whether they can roll. And for shapes to roll, we know they need to have a curved surface. Whether they can stack — we’ve learned that to do this, we need flat surfaces at both ends. Or whether they can slide — and to do this, we’ve learned that a 3D shape needs a flat surface to slide on.