Hands on the clock
The clock's hands sweep out angles all day: at 3 o'clock they make a square 90° corner, at 6 o'clock a straight 180° line. Classifying angles by how far they turn is just reading how open those hands are.
Measuring a turn
An angle measures the turn between two rays meeting at a point. Acute angles are less than 90°, a right angle is exactly 90°, obtuse angles are between 90° and 180°, and a straight angle is 180°.
Simulation · Angle explorer
60° — acute
Drag the angle open and closed and watch its name change at 90° and 180°.
Lab · Name that angle
- Open the angle to 45° — is it acute, right, or obtuse?
- Set it to exactly 90°.
- Push past 90° toward 150°.
What you should see: 45° is acute, 90° is a right angle, and 150° is obtuse. The label updates as you cross each threshold.