Different Types of Angles


Lesson Planning of Right, Acute and Obtuse Angles

Subject Mathematics

Grade 4th

Students` Learning Outcomes

  • Recognize right angle through horizontal and vertical lines.
  • Demonstrate acute and obtuse angles through right angle.

Information for Teachers

  • Types of angles: Zero angle, Straight angle, Obtuse angle, Right angle, and Acute angle.
  • Angles are classified according to their degree (size).
  • An acute angle is greater than 0° and less than 90°.
  • A right angle equals exactly 90°.
  • Note that a right angle is marked on the diagram as a small square on the point “B”.
  • An obtuse angle is greater than 90° and less than 180°.
  • A straight angle equals exactly 180°.

Material / Resources

Writing board, chalk/marker, duster, toothpicks, glue, clock (paper made or original), textbook


  • Act and demonstrate by sitting in three directions: as;
  1. Straight up,
  2. Bend down,
  3. Stretch back and hence introduce right, acute and obtuse angles respectively.
  • Draw figures on board and tell them that L is right, V is acute angle.
  • Clock hands work well for playing with angles, 3 o`clock and 9 o` clock represent right angles between the hour and minute hand and 2 o`clock shows an acute angle, 4 o`clock shows an obtuse angle, 9 o`clock shows straight angle.



Activity 1

  • Movement of arm along with elbow reinforce acute and obtuse along straight line.
  • Repeat to explain the difference from right angle.
  • Let them use their arms and legs to make angles by bending and moving. (collect of sketch physical exercise pictures if possible)
  • Make the angles with toothpicks, glue them on the paper, and label them.
  • Find five objects in your home that have right angles in them.
  • Draw some angles on the board and ask them to mark the angles as acute, right, obtuse, or straight (whole class activity).
  • Recall the concept of horizontal and vertical lines and introduce the angle between them as right angle by asking does it make L shape?
  • Assign pair work of labeling angles (questions can be assigned from book or prepare a worksheet).
  • Invite one or two students to recap the points discussed today.
  • Collect students work to check later.


Sum up / Conclusion
  • Acute angle is between 0° and 90°.
  • Obtuse angle is between 90° and 180°.
  • Right angle is of 90°.
  • Straight angle is of 180°.


  • 78° is either acute or obtuse angle?
  • 137° is either acute or obtuse angle?
  • The right angle is of ___________ degree.
  • Can someone show me a right angle?
  • Can someone show me an acute angle?
  • Can someone show me an obtuse angle?

Follow up

  • Open a door, measure angle from floor and write its type after 5 seconds.
  • Ask each student one by one to make different angles shape by stretching their arms.
  • Match the following angles with their names:






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