An angle is simply a measure of turn between two lines that meet at a point (vertex). Instead of using plastic protractors right away, I start our geometry unit by having students find angles in the classroom.
1. The Right Angle (90°)
A right angle forms a perfect "L" shape, like the corner of a textbook, a door frame, or a sheet of paper. Whenever you see a square symbol in a corner, it means exactly 90 degrees.
2. Acute Angles (< 90°)
Mnemonic: Think "A cute little angle"! Acute angles are sharper and narrower than a right angle (between 0° and 89°). Examples: a slice of pizza, scissors cutting paper, or a half-closed laptop.
3. Obtuse Angles (> 90° and < 180°)
Obtuse angles are wide, open angles larger than a right angle. Examples: a reclining beach chair, an open book resting on a table, or clock hands at 4:00.
4. Straight Angle (180°)
A straight line that forms a flat 180 degrees, like a ruler or outstretched arms.