In grade three, students should know that perpendicular lines cross, or will cross if they are extended, at a right angle. Learners should understand that a right angle is the same as a 90 degree angle and eventually be able to measure this with a geometric compass.The grade three math curriculum also includes distinguishing between perpendicular, intersecting and parallel lines. For fun, you can encourage students to find real-world two and three-dimensional examples of perpendicular lines.

- Skill level:
- Moderately Easy

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### Things you need

- Large teacher's compass
- White or black board
- Compass for each student
- Worksheets

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## Instructions

- 1
Draw a right angle (90 degrees) on the board; draw a small square in the area where the vertical and horizontal lines meet. Tell the students that this is a 90 degree angle and that it is called a "right angle;" tell them the square symbol means it is a right angle and since the lines meet or would cross at 90 degrees they are perpendicular.

- 2
Draw two lines that are perpendicular to one another but that do not meet. Ask the students if these lines are perpendicular like the last example. Explain to them that they are perpendicular because if you extended them they would eventually meet and cross at a 90 degree angle.

- 3
Ask students to walk around the class and find examples of perpendicular lines. Explain by saying they should look for examples of a perfectly horizontal line or face meeting or crossing a perfectly vertical line or face. Examples they may find include, the door is perpendicular to the floor, the length and width of a text book, and the table width to its legs.

- 4
Take students on a walk outside the school and ask them for to look for examples of perpendicular lines in the real world, such as the lines on a tennis court, a rectangular sign or a street corner.

- 5
Draw perpendicular lines on the board, including the right angle square symbol, and show them how to confirm it is a 90 degree angle by using a teacher's-size compass.

- 6
Provide students with a worksheet of various pairs of lines that are intersecting. Ask students to determine which pairs of lines are perpendicular by measuring the intersection angle with their compass.

- 7
Discuss the worksheet with students by bringing up the differences between intersecting and perpendicular lines. Intersecting lines meet and cross at any angle; perpendicular lines are intersecting lines that only meet and cross at a right angle.

- 8
Teach students about parallel lines. Drawing them on the board, and explain these are lines that move in the same direction but never cross.

- 9
Provide students with a worksheet where they have to identify whether pairs of lines are intersecting, parallel or perpendicular.