When you open a door, turn a doorknob, or turn right around a corner, you are making a turn. The size of this rotation is what we call angle.

How much did you spin?

  • One ​​full turn: you turn until you look at the same place again.
  • Half turn: you turn your back to where you were looking.
  • Quarter turn: you turn to the side, like a corner. This rotation forms a right angle.

Mathematicians divide the entire revolution into 360 equal parts, called degrees (°). So half turn has 180°, and a quarter turn has 90°.

Move the control or use the buttons. The blue pointer rotates from the gray pointer.

Acute, straight and obtuse

DefiniçãoThree types of angle

  • Right angle: a quarter of a turn (90°). It’s the corner of a sheet of paper.
  • Acute angle: smaller than the straight angle. Reminds me of the tip of a slice of pizza.
  • Obtuse angle: greater than the straight angle and less than half a turn. Reminds me of a wide open fan.
Classify the angle. Use the corner of a sheet to check!

Angles on the clock

The hands of a clock form angles. At 3 hours, they form a right angle. At 6 hours, form a half turn. At 1 time, they form an acute angle.

Check the answer

At 9 hours, an angle straight (a quarter turn). At 5 hours, an angle obtuse (150°). At 2 o'clock, an angle acute (60°).

True or false?

  1. Half a turn is 180 degrees.
  2. An acute angle is greater than a right angle.
  3. The corner of a door forms a right angle.
  4. Anyone who turns twice ends up looking at the same place.