Acute, right, obtuse, straight or reflex?
Measure ten angles, from the hands of a clock to an open laptop and a pizza with a slice gone, compare each with a right angle, and sort them by type.
Core concept
In short: Turn two lines to make angles, then sort them by size: small, square, wide or more than a straight line.
Angles are measured in degrees: acute angles are less than 90°, a right angle is 90°, obtuse angles are between 90° and 180°, a straight angle is 180°, and reflex angles are more than 180°
Topic: Lines and angles
An angle: The amount of turn between two lines that meet, measured in degrees (°). All key words is made where two lines (arms) meet at a point (the vertex). Its size is how far one arm has turned from the other, measured in degrees (°) with a protractor. A full turn is 360°. A quarter turn, like the corner of a book, is 90°: a right angle. Angles smaller than a right angle are acute. Angles bigger than a right angle but smaller than a straight line are obtuse. A straight line makes a straight angle of 180°. Angles bigger than 180° are reflex. The hands of a clock make every kind: at 3 o'clock they make a right angle, and each hour mark is 30° apart.
What you will learn
- Measure angles in degrees.
- Classify angles as acute, right, obtuse, straight or reflex.
- Find the angle between the hands of a clock.
- Find angles in everyday objects.
Before you start
- Know that a full turn is 360°.
Materials
- A paper clock with moving hands
Equipment
- A protractor
Procedure
- Pick a card and measure its angle.
- Compare it with a right angle.
- Do this for at least six angles, then sort them all.