Video Transcript
Angles
In this video, we’re going to learn
how to identify and name acute angles, right angles, and obtuse angles.
An angle is the amount of turn
between two straight lines or rays, which meet at a vertex or point. We call the sides of an angle the
arms. We measure angles in degrees, and
this is the symbol we use to write degrees. A complete turn is 360 degrees. And if we make half a turn, we’ve
turned 180 degrees. And a quarter of a turn is 90
degrees. Angles which have a square corner,
like this angle, are called right angles. A right angle measures 90
degrees. An angle which measures less than
90 degrees is called an acute angle. An angle which measures more than
90 degrees but is less than a straight line is called an obtuse angle.
You could have a go at making some
angles of your own. You could use craft pipe
cleaners. Which angle have we made? It’s a right angle. Can you see it has a square
corner? Which kind of angle is this? It’s less than a right angle. Can you remember its name? It’s an acute angle. This angle is greater than a right
angle. Can you remember its name? It’s an obtuse angle. We can tell if an angle is acute or
obtuse by comparing it to a right angle.
We can make our own right-angle
corner using a piece of paper. And we can use this to check if an
angle is less than or greater than a right angle. First, we need to fold the piece of
paper in half and then fold it in half again. We’ve made a right-angle
measure. We can use our right-angle measure
to tell if an angle is greater than or less than a right angle. This angle is greater than a right
angle, which means it’s an obtuse angle. By matching the corner of our
right-angle measure with the vertex of this angle, we can see the angle measures
less than a right angle. So, we know that this is an acute
angle because acute angles measure less than a right angle.
Let’s try some questions now to
help us practice identifying acute angles, right angles, and obtuse angles.
Determine the type of angle
highlighted in orange. Is it a right angle, an obtuse
angle, or an acute angle?
In this question, we have to
identify the type of angle which is highlighted in orange. Is this angle a right angle? We could use a right-angle measure
to check. We simply need to place the corner
of our right-angle measure into the corner or vertex of the angle. Now, we can see the orange angle
measures more than a right angle. What do we call an angle which is
greater than a right angle? Can you remember what an obtuse
angle is? This is an obtuse angle. It measures more than a right
angle.
The angle highlighted in orange
measures more than 90 degrees, so it’s an obtuse angle. Acute angles measure less than a
right angle. The type of angle highlighted in
orange is an obtuse angle.
Determine the type of angle
highlighted in orange. Is it a right angle, an obtuse
angle, or an acute angle?
In this question, we have to
identify which type of angle the orange angle is. Is this angle a right angle? We’ve drawn the arms of the
angle. This is a right angle. The orange angle is less than a
right angle. An obtuse angle is an angle which
measures greater than 90 degrees. The orange angle is not an obtuse
angle. The angle highlighted in orange is
an acute angle. It measures less than a right
angle. The type of angle highlighted in
orange is acute. The orange angle is an acute
angle.
Which of these is an acute
angle? Angle 𝐴, angle 𝐵, or angle
𝐶.
In this question, we have to
identify the acute angle. It can’t be angle 𝐵 because it’s a
right angle. This is the symbol we use to show a
right angle. We need to use our knowledge of
angles to help answer this question. We know that an acute angle is less
than a right angle. Does angle 𝐴 or angle 𝐶 measure
less than a right angle? We could use a right-angle measure
to help. Angle 𝐴 measures less than a right
angle. The angle which is an acute angle
is angle 𝐴 because it measures less than a right angle. Angle 𝐵 is a right angle, and
angle 𝐶 is greater than a right angle. Angle 𝐴 is an acute angle.
Look at the given shape. How many acute angles are there in
the shape? How many obtuse angles are there in
the shape? How many right angles are there in
the shape?
In this question, we have to count
the number of acute angles in the given shape, the number of obtuse angles, and the
number of right angles. We can answer the third part of the
question really quickly. This blue square is the symbol we
use to show a right angle, so we know the shape has one right angle. How many acute angles are
there? We know acute angles measure less
than 90 degrees or less than a right angle. This is an acute angle, and this is
an acute angle. Both of these angles measure less
than a right angle. This angle is greater than a right
angle. We call this type of angle an
obtuse angle. So, there are two acute angles, one
obtuse angle, and one right angle in the given shape.
What have we learned in this
video? We’ve learned how to identify right
angles using a right-angle measure. We’ve learned that acute angles
measure less than a right angle. And we’ve learned that obtuse
angles are greater than a right angle.
