A child happily drawing a colorful town map at a desk

Map Maker Geometry

Ava is designing a map of her town. Streets, paths, and corners hide a secret: they are all made of geometry!

4th Grade Math

Step 1: Know Your Lines

A line goes on forever in both directions. A line segment stops at two endpoints. Ava draws this figure with one endpoint and one arrow. What did she draw?

A ray starts at one endpoint and goes on forever in one direction. The arrow shows it never stops.

Step 2: Streets That Never Meet

Ava draws two straight streets. They stay the same distance apart forever. No matter how far they go, they will never cross. What are these lines called?

Parallel lines never meet. Perpendicular lines are different: they cross and make square corners.

Let's Remember

The Building Blocks of Geometry

          A point is one exact spot.

          A line goes on forever both ways.

          A segment stops at two endpoints.

          A ray has one endpoint and goes on forever.

          Perpendicular lines cross at square corners.

Step 3: Angles Have Sizes

Two rays that share an endpoint make an angle. We measure angles in degrees. This angle makes a perfect square corner. What is it called?

A right angle makes a square corner and measures exactly 90 degrees. Acute angles are smaller than 90. Obtuse angles are bigger than 90.

Watch Out!

long rays, SMALL angle

short rays, BIG angle

Common Mistake

          Longer rays do NOT make a bigger angle!
          An angle's size is the opening between its rays.
          Can you distinguish the opening from the ray length?
        

Name That Angle!

This angle opens wider than a square corner. What kind of angle is it?

This angle is obtuse because it opens wider than 90 degrees. Acute angles open less than 90 degrees.

Crossing Streets

Two streets on Ava's map cross and make square corners. What are these lines?

Perpendicular lines cross and form right angles. Parallel lines never cross at all.

Word Problem

Ava draws a straight path from the school to the library. The path starts at one point and stops at another point. What did she draw?

A line segment has two endpoints. The path starts and stops, so it is a segment, not a line or a ray.

What Goes in the Blank?

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A right angle = ? degrees

A right angle measures exactly 90 degrees. Less than 90 is acute. More than 90 is obtuse.

Angles in Figures

This rectangle is the park on Ava's map. Count the right angles inside it.

A rectangle has 4 right angles, one at each corner. It also has 2 pairs of parallel sides!

Challenge Time!

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At one crossing, an angle measures 91 degrees. At another, an angle measures 89 degrees. Which statement is true?

Only exactly 90 degrees is a right angle. 91 is more than 90, so it is obtuse. 89 is less than 90, so it is acute.

Look around your neighborhood. Where do you see parallel lines, perpendicular lines, or right angles?

Great Work!

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correct

angle degree parallel perpendicular distinguish