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Perpendicular Lines

Lines that intersect at 90 degree or right angles.

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Turning The Tables
Teacher Contributed

Credit: Martin Pettitt
Source: http://www.flickr.com/photos/95012874@N00/2521374167/
License: CC BY-NC 3.0

Imagine a world where every time you try to sleep, you roll off the bed. When you put your dinner on the table, the plate slides to the floor. Staying in your chair is a constant battle, and you must walk up and down hills as you cross your house. Imagine a world without perpendicular lines.

Why It Matters

Carpenters, builders, and furniture makers depend on perpendicular lines to create flat surfaces and buildings that stand up straight. In order to create perfect corners and straight edges, woodworkers use a tool called a square. This tool helps them create perfectly square, or 90 degree, angles.

Credit: Laura Guerin
Source: CK-12 Foundation
License: CC BY-NC 3.0

Since two lines meeting at a 90-degree angle are perpendicular, your house, neighborhood, and classroom are full of perpendicular lines. Perpendicular lines help ensure that your table top is flat. They mean that the drawers on your dresser can open and close easily and that doors stay shut when you close them. Many older houses become less square as they age. Good carpenters know tricks to make a crooked door hang straight and square again.

See for yourself: http://www.thisoldhouse.com/toh/video/0,,1639467,00.html

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Watch this video to see how a carpenter uses his square to create straight lines and 90 degree angles. Then answer the question below.


Why is it important for carpenters and builders to create square angles and perpendicular lines?

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Image Attributions

  1. [1]^ Credit: Martin Pettitt; Source: http://www.flickr.com/photos/95012874@N00/2521374167/; License: CC BY-NC 3.0
  2. [2]^ Credit: Laura Guerin; Source: CK-12 Foundation; License: CC BY-NC 3.0

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