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.
