### Video Transcript

Properties of 2D Shapes

In this video, we’re going to look
carefully at 2D or flat shapes to see what features a shape always has and what
features it sometimes or never has.

Oh dear! This is not good. 30 seconds into the video and we’ve
already got a mistake. This isn’t a triangle, is it? It’s a square. But how do we know it’s a
square? What makes a square square? And what makes a triangle not a
square? These sorts of questions might
sound funny, but they’re really important because if we want to spot a square every
single time we see one, we need to know what makes it a square. And there are three ideas we can
use to help us.

These are the words “always,”
“sometimes,” and “never.” Let’s see how these words can help
us. Our picture shows an orange
square. Now, can we say squares are always
orange? Remember, the word “always” means
every single one. Of course not. We can have blue squares, pink
squares, or even red spotty squares. Squares are not always orange;
they’re sometimes orange. The color of a square isn’t what
makes it a square. The same is true of the size of a
shape. Squares aren’t always this
size. They’re only sometimes this
size. Sometimes they’re smaller;
sometimes they’re larger. We can’t spot a square by its
size.

I hear you say, “I think I’ve
spotted something.” Every single one of these squares
has got a side that goes across from left to right at the top, one that does the
same at the bottom. And they all have two sides that go
straight up and down. Squares are always in the same
position. Not if we turn them. We can see that a shape’s color,
its size, and the position that it’s in are not really important when it comes to
spotting what shape they are. The really useful word that we need
to think about here is the word “always.” When we use this word, we mean
every single time. What makes this shape a square are
the things that every single square has in common.

And with 2D shapes, we need to look
at things like the number of straight sides that a shape has and the number of
vertices or corners. This square has four straight
sides. We can show this by putting a
plastic counter on each one just so we don’t miss any out. One, two, three, four. Can we say all squares have four
straight sides? Yes, we can. Not only that, but they’re all the
same length, aren’t they? So another always statement, one of
these things that makes a square a square is that all squares have equal sides.

What about the number of vertices
that a square has? Let’s count the corners on our blue
square. One, two, three, four. Can we say all squares have four
vertices? Yes, we can. Every single square ever has always
had four corners. Without four corners, it wouldn’t
be a square. And this is where we can think
about the idea “never.” We could use our all statements to
write some never statements. If we know that all squares have
four straight sides, then we can say squares never have any curved sides.

And if we know that all squares
have four corners, we could say squares never have more than four corners. If we’re going to go shape
spotting, we don’t want to be looking at the color or the size or the position of a
shape. We need to look for the features
that all shapes of that type have in common, things like the number of straight
sides and the number of corners. Let’s try answering some questions
now where we have to put into practice the ideas of always, sometimes, and
never. Let’s go shape spotting.

Fill in the blanks in the following
sentences about triangles. All triangles what. Have more than three sides, are
yellow, or have three sides. But only some triangles what. Have three corners, are green, or
have three straight sides.

This question is all about the 2D
shape, the triangle. And we’re given some pictures to
help us. We’re given two very short
sentences to complete. Did you notice the main difference
between them? There are two very small words, but
they make a lot of difference. In the first sentence, it’s the
word “all.” This means everything, doesn’t it,
every single one. So to complete this sentence, we’re
looking for a feature of triangles that every single triangle has. This is going to be one of the
things that makes a triangle a triangle.

Now, the small word in our second
sentence is the word “some.” This word is different because it
means not all, part of the whole amount. And when we complete this sentence,
we’re looking for a feature that not every triangle has in common, only some of them
do. Let’s start with our first sentence
then. All triangles what. Can we say that all the triangles
in the picture and all the triangles we could ever draw have more than three
sides? If we count the number of sides
that our first triangle has, there are one, two, three.

We can use the picture to help us
here. And we can say that all of the
triangles in the picture do have three sides. And even if we were to draw some of
our own, they would also have three sides. We can’t say all triangles have
more than three sides, can we? We can’t even say some triangles
have more than three sides. We’d have to say, no triangle ever
has more than three sides.

Now, what about the color of these
shapes? Can we say all triangles are
yellow? Although one of our triangles in
the picture is a yellowy-orange color, we know that triangles can be any color. They could be pink, green, or
white, like in the picture. But they could also be blue stripy
or shiny silver. I suppose we could say some
triangles are yellow. The color of a triangle isn’t
something that makes it a triangle. Now, we’re only left with one
possible answer. All triangles have three sides. Well, we don’t need to think too
much about this, do we? We’ve already talked about the fact
that every single triangle has got three straight sides. We can say all triangles have three
sides.

Now let’s think about our second
sentence. But only some triangles what. Do only some triangles have three
corners. Well, we can see on our first
triangle in the picture that it does have three corners. In fact, so do all the others. This isn’t something that only some
triangles have. This is something that’s true of
every triangle. It’s one of those features that
makes a triangle a triangle. We could actually use this phrase
in our first sentence, “All triangles have three corners.” Let’s try our second phrase. Can we say only some triangles are
green? Yes, we can, can’t we?

As we’ve said already, triangles
can be any color. Of course, only some triangles are
green, knowing the color of a shape doesn’t help us identify what sort of a shape it
is at all. And let’s just check our last
phrase. Only some triangles have three
straight sides. Not at all. As we’ve found out already, all
triangles have three straight sides. In this question, we’ve thought
about the things that are always true of triangles and the things that are sometimes
true. And this helped us complete the
sentences. All triangles have three sides. But only some triangles are
green.

Anthony has sorted these shapes
into two groups, group one and group two. Why does this shape belong in group
one? Because it is green, because it has
more than four sides, or because it is a rectangle.

We can tell by reading this
question that Anthony has done some shape sorting here. He’s had some 2D shapes, and he
sorted them into two groups. Now, this question is really
interesting because it gets us thinking about what different 2D shapes have in
common. In particular, we’re thinking about
the 2D shapes that are in group one because we’re given a picture of a shape and
we’re asked, why does it belong in group one? Can you see it in group one? Looks like this shape here, doesn’t
it? And why has Anthony decided to put
this particular shape with all the others in group one?

Is it because it’s green? Well, you can understand why
somebody might think this was the right answer. It is a green shape, and all the
other shapes in group one are also green. So do you think the rule for
putting a shape in group one is that they’re green? No, because if we look in group
two, we can see a green circle and a green triangle. Just because some shapes are the
same color doesn’t mean they’re the same type of shape at all. Anthony hasn’t sorted these shapes
by color, has he?

Now, do you think this shape
belongs in group one because it has more than four sides? Well, if we actually count the
number of sides that this shape has, we can see that it has four sides, not more
than four sides. So this statement isn’t true at
all. Now, this is where the question
gets interesting because if this statement said, because it has four sides, it still
wouldn’t be the right answer. Can you see that one of the shapes
in group two also has four sides?

Anthony hasn’t chosen to sort these
shapes based on the number of sides that they have. This only leaves us with one
possible answer. This shape belongs in group one
because it’s a rectangle. And Anthony has sorted out all the
rectangles and put them all together in group one. And if we look at all the shapes in
group one, there are some features that they all have in common. These are the things that make them
rectangles. Each one of them has four square
corners. And they all have four straight
sides. These are the things Anthony was
looking for when he wanted to sort these shapes into group one, not the fact they
were green. This shape belongs in group one
because it is a rectangle.

There is a mystery shape in this
bag. Which clue will not help you guess
the name of the shape? It has five corners, it is green,
or it has five straight sides. Based on these clues, what is the
shape in the bag? Is it a square, a triangle, or a
pentagon?

Are you feeling like a shape
detective? Well, you’re going to need to be
one with this question because we’re told we have a mystery shape in the bag. And like any detective, we’re given
some clues to help us solve the problem. But not all of the three clues are
useful. We’re asked, which clue will not
help you guess the name of the shape? Now, all these clues are true about
our shape, but not all of them are useful. The first clue talks about the
number of corners that our shape has. The second clue talks about its
color. And our third clue talks about the
number of straight sides that it has. Which one of these clues isn’t very
useful at all?

It’s the color, isn’t it? Knowing the color of a shape
doesn’t help us tell what it is. Some circles are green, some
triangles are green, any shape at all could be green. Knowing that the shape is green is
not going to help us at all. If we want to be true shape
detectives, we need to use clues like the number of corners that a shape has, and
here we’re told that it has five corners, and also the number of straight sides that
it has, and we’re told that it has five straight sides. In the second part of the question,
we need to put these clues to the test.

Based on these clues, what is the
shape in the bag? Is it a square, a triangle, or a
pentagon? Now, one shape might jump out
straightaway as being wrong. We can see straightaway that the
triangle is the only shape that isn’t green. So we do know that the answer is
not going to be the triangle. But it would be a shame if we cross
the triangle off our list straightaway just because it was the wrong color. As we’ve said already, the color of
a shape isn’t something we can rely on.

So let’s think of our two clues
that really matter. It has five corners, and it has
five straight sides. How many corners does a square
have? One, two, three, four corners, not
five. And we also know that a square has
one, two, three, four straight sides, not five. The shape in the bag is not the
square. As we’ve already said, we know that
the shape isn’t the triangle cause it’s red. But let’s look at the more
important clues. Triangles have three corners, not
five, and three sides, not five.

This only leaves us with the
pentagon. A pentagon, it’s a shape that has
one, two, three, four, five corners. And we can count one, two, three,
four, five straight sides. Of course, the pentagon is green as
well. But it’s not this clue that helped
us. As any good shape detective knows,
we can tell a shape by the number of straight sides that it has and the number of
corners or vertices that it has. The clue that did not help us guess
the name of the shape was, it is green. So we used the remaining two clues,
it has five corners and it has five straight sides, to help us identify the mystery
shape as the pentagon.

What have we learned in this
video? We’ve learned how to look carefully
at 2D shapes to see what features a shape always has, sometimes has, or never
has.