Original notes — ready
Chapter 3: Angles as Turns
CBSE (NCERT, English Medium) • Class 5 • Mathematics • Book: Math Mela
Angles as Turns — EG's own notes, in simple words
Book: Math Mela (CBSE, Class 5) | Chapter 3 | Medium: English
Diagram (labels are printed on the image): A protractor, a clock at 3 o'clock and a turning dancer. A general teaching picture about angles as turns.
Children making angles with their arms. A general picture about turns.
What the chapter is about
An angle is a turn. When you turn your body a little, you make a small angle; when you turn fully around, you make a big angle. A full turn is 360 degrees.
A quarter turn (like turning to face the next wall of a room) is a right angle: 90 degrees. A half turn is 180 degrees. Angles smaller than 90 degrees are acute; angles bigger than 90 degrees but smaller than 180 degrees are obtuse.
We see angles everywhere: in the hands of a clock, in the corner of a book, in the opening of a door, and in the turn of a dancer.
Dancers, drivers and players all use turns. A driver turning left at a corner makes a quarter turn, and a dancer spinning fully around makes a full turn. Angles are not only in books — they are in every turn your body makes.
What you should learn
Stand and turn your body: quarter turn, half turn, full turn. Feeling the turn makes the degrees easy to remember.
Key Terms
- Angle — The amount of turn between two lines.
- Degree — The unit for measuring angles, written °.
- Right angle — A quarter turn: 90°.
- Acute angle — An angle smaller than 90°.
- Obtuse angle — An angle bigger than 90° but smaller than 180°.
- Protractor — A tool used to measure angles in degrees.
Remember
- Full turn = 360°; half turn = 180°; quarter turn = 90°.
- Right angle = 90°.
- Acute < 90° < obtuse < 180°.
- A clock's hands make angles as time passes.
Exam Tip / Common Mistake
Common mistake: calling every corner a right angle. Check with a quarter turn: only a 90° corner is a right angle.
Chart / Table: Types of angles
| Angle | Size |
|---|---|
| Acute | Less than 90° |
| Right | Exactly 90° |
| Obtuse | Between 90° and 180° |
| Straight | Exactly 180° |
Think and try
Stand up and turn: quarter turn to your right, then another quarter turn. How many degrees have you turned in all? Now turn back to face where you started. How many quarter turns did that take?
Practice set — try it yourself
- How many degrees is a quarter turn?
Hint: A full turn is 360°. - Is 60° acute or obtuse?
Hint: Compare with 90°. - What angle do the clock hands make at 3 o'clock?
Hint: Think about a quarter turn. - How many right angles are in a full turn?
Hint: Divide 360 by 90. - Draw and label one acute, one right and one obtuse angle.
Hint: Use a protractor or the corner of a book to check.
How to use this page: Read the summary, say the Key Terms in your own words, then try the practice set without looking. Ask your teacher or parent to check your answers.