Video: Identifying 3D Shapes That Stack, Slide, or Roll

Which group does this shape belong to? [A] Cannot slide [B] Can slide

01:54

Video Transcript

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.

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