Turns everywhere
A turn happens whenever something rotates around a fixed point. Stand on one spot and spin once , that is a full turn. Spin halfway and stop , that is a half turn. Spin only a quarter , a quarter turn.
What is this?
An angle is the amount of turn between two arms that meet at a point. The point where they meet is called the vertex, and the two lines coming out are the arms.
Picture a clock. The two hands meet at the centre , that is the vertex. As the minute hand moves, the angle between the two hands changes. From 12 o'clock to 3 o'clock, the minute hand makes a quarter turn. From 12 to 6 it makes a half turn. From 12 all the way back to 12 it makes a full turn.
We can measure turns in special units called degrees, written °. A full turn is 360°. So:
- Full turn = 360°
- Half turn = 180°
- Quarter turn = 90°
- An eighth of a turn = 45°
When the angle is small (very little turn), we call it an acute angle. When it is a quarter turn, we call it a right angle. When it is bigger than a quarter turn but smaller than a half turn, it is obtuse.
Turns are everywhere in the world around you , the steering wheel of a car, the dial of a fan, the open page of a book, the slice of cake on your plate.
Worked examples
Example 1. From 12 o'clock to 3 o'clock, how much does the minute hand turn?
- 12 → 3 is one-quarter of the clock face.
- That is a quarter turn = 90°.
Example 2. A door is fully open at a half turn and closed at zero turn. How many degrees does it move when fully opened?
- Half turn = 180°.
Example 3. Anish spins around once and stops. How many degrees did he turn?
- One full turn = 360°.
Try it
- From 12 to 6 on a clock, how much does the minute hand turn?
- How many right angles in a full turn?
- Is a quarter turn smaller or bigger than a half turn?
- Draw an angle that is roughly a quarter turn.
- How many degrees is the angle of half a turn?
Hands-on
Body spin. Stand on the floor, mark your front direction. Spin a quarter turn to the right. Where are you facing now? Spin another quarter turn. Now? Keep going until you complete a full turn.
Clock turns. Look at a wall clock at the start of an hour. Note where the minute hand points. After 15 minutes, look again. The minute hand has made a quarter turn , see for yourself.