Video Transcript
Angles and Right Angles
In this video, we will learn how to
recognize and define angles, identify right angles, and say whether angles are
bigger or smaller than a right angle. An angle is formed by two straight
lines sharing an endpoint. We can also call an endpoint a
vertex.
How many angles can you count in
this shape? Here’s one angle. We’ve drawn the two lines that meet
at a point to create this angle. Here’s our second angle. There’s a third angle and a
fourth. This shape has four angles. How many angles does this triangle
have? One, two, three. Did you notice that the word
triangle contains the word angle? A triangle means a shape with three
angles. The prefix tri- means three.
How many angles does this shape
have? One, two, three, four. This shape has two special angles
called right angles. A right angle is an angle that
forms a square corner. Some angles, like this one, measure
less than a right angle. And other angles, like this one,
are bigger than a right angle. We can use a set square to help us
identify right angles. We simply place the square corner
of the set square into the angle we want to measure. If the square corner fits neatly
inside the angle, as it does in this case, then we know the angle is a right angle
because a right angle is an angle that forms a square corner.
If you don’t have a set square, you
could make your own right angle tester using a piece of paper. All you need to do is fold your
piece of paper in half, like so, and then fold it in half again. Now you have your very own right
angle tester. Let’s practice using it to see if
we can find any more right angles in our shape.
Our right angle tester fits really
neatly into this angle. So we found another right angle in
our shape. Our shape has two right angles. We can also use our right angle
tester to test if an angle is bigger or smaller than a right angle. By placing our right angle tester
in this angle, we can see that this angle is smaller than a right angle. And by placing our right angle
tester into this angle, we can see the angle is bigger than a right angle. So we’ve learned that this shape
has four angles. Two of these angles are right
angles. One angle is bigger than a right
angle. And the other is smaller than a
right angle.
Let’s practice what we’ve learned
about angles by answering some questions.
Which of the following shapes has
four angles?
In this question, we’re shown four
different shapes. We have to select the shape which
has four angles. Let’s start by looking at this
shape. We know angles are formed by two
lines which share an endpoint. Here’s one angle, two, three. Our first shape has three
angles. How many angles does this shape
have? One, two, three, four, five. The shape has five angles. Let’s count the number of angles
the third shape has. One, two, three, four, five,
six. So this must be the shape which has
four angles. Let’s quickly check. Yes, it does have four angles. This is the shape which has four
angles.
Pick the shape that Emma is
describing. “It has five angles. Three of the angles are right
angles.”
In this question, we’ve been shown
four different shapes. We have to pick the one which has
five angles and three of those angles are right angles. Which of our shapes has five
angles? Let’s count the number of angles
the first shape has. Here’s one, two, three, four,
five. Does this shape have three right
angles? No, it doesn’t.
How many angles does our second
shape have? A square has four angles. Emma’s looking for the shape which
has five angles, and three of those angles should be right angles. This is not the shape that Emma is
describing. How many angles does our third
shape have? Here’s one, two, three, four,
five. This could be the shape that Emma
is describing.
Does it have three right
angles? We can check using our right angle
tester. A right angle is an angle that
forms a square corner. So our shape has five angles, and
we know that one of them is a right angle. Here’s a second right angle. Here’s another. This shape does have three right
angles. So this is the shape that Emma is
describing. It has five angles and three of the
angles are right angles. This shape is a pentagon. It has five sides and five
angles. But none of its angles are right
angles. We picked the shape that Emma is
describing. It has five angles and three of
them are right angles.
Complete using “more” or “less”:
The given angle is more or less than a right angle.
In this question, we have to
compare the angle we’ve been given to a right angle. Is this angle more or less than a
right angle? A right angle is an angle that
forms a square corner. To help us decide if the given
angle is more or less than a right angle, we could use this set square. This corner of the set square is a
right angle. So if we place our set square into
the angle we’ve been given, we can see if our angle is a right angle. There we go. The given angle is smaller than a
right angle. So the missing word is “less.” The given angle is less than a
right angle. We completed the sentence using the
word less.
What have we learned in this
video? We have learned that an angle is
formed by two lines sharing an endpoint. We also learned that a right angle
is an angle that forms a square corner. And finally, we learned how to tell
if an angle is bigger or smaller than a right angle using a set square or a right
angle tester.
