Angles and measuring them in degrees
📖 In short
Open a pair of scissors a little, then more: the gap between the blades is an angle that gets bigger and smaller. An angle is the opening between two lines that meet at a point called the vertex. We measure it in degrees with a tool called a protractor, and write degrees like this: °.
🤩 Did you know?
- A full turn is 360 degrees, and the Babylonians may have chosen this number because a year is about 360 days.
- At 3 o'clock the hands make a right angle: 90 degrees.
- When a skier jumps and spins all the way round, we say they did a 360.
- Bees build their cells with angles of 120 degrees each.
🔎 Find out more
🌟 Right angle
The corner of a sheet of paper, the corner of a book and where the wall meets the floor are all right angles of 90°. We mark one with a little square at the vertex and check it with a set square.
🔍 Acute and obtuse
An angle smaller than a right angle is acute, like the tip of a pizza slice. One bigger than a right angle but smaller than 180° is obtuse, like the back of a chair leaning backwards.
💡 Straight angle and full turn
If the angle opens until the two lines make one straight line, it's a straight angle of 180°. And if the line turns all the way round back to where it started, it has turned 360°.
🎯 Angles on a clock
A clock's hands make angles: at exactly three o'clock a right angle, and at six o'clock a straight angle. Each hour on the clock face is 30°.
📊 See it in a picture
🧮 Worked examples
- 90° + 90° = 180°Two right angles make a straight angle.
- 4 × 90° = 360°Four right angles make a full turn, like the corners of a square.
- 3 × 30° = 90°Between 12 and 3 o'clock there are three hours, each 30°.
📚 Key words
- Angle
- The opening between two lines that meet at a point
- Protractor
- A half-circle tool for measuring angles in degrees
- Right angle
- An angle of 90 degrees, like the corner of a sheet of paper
🧪 Try it at home
Fold a piece of paper twice to make a paper “right angle”. Use it to test the corners of things at home: the table, the door, a book. Which are right angles? Which are acute or obtuse?
🧩 Test yourself
1 How many degrees is a right angle?
2 An angle measures 130°. What kind is it?
3 What do we measure an angle with?