Why Does the Earth Look Flat?

OBJECTIVES: Students will demonstrate that by increasing the number of sides of a regular polygon they will approximate a circle. Students will demonstrate that segments (arcs) of a very large circle can appear straight.


  • 50+ planks per group


  1. Divide the class into small groups. Ask each group to form a closed figure approximating a circular shape with 8 planks (flat construction).

  2. Next, form a circular shape with 12 planks. Then with 16 planks. Ask, “What do you notice?” [The shapes are looking more and more like a circle.]

  3. Form a circle with 40 planks. This will be a circle about 5 feet in diameter. Students will probably reach the right size by trial and error.

  4. Ask the students to imagine that they were a ladybug or ant crawling on one of the KEVA Planks. How would a bug describe the shape of the perimeter from its perspective? [Close to flat.] What is the actual shape? [Curved.]

  5. Ask the class to imagine a circle made of 100 planks. How big would it be? [About 12 feet in diameter.] Students should be able to note that the curve of the circle would not be as sharp. Imagine a circle built with 1,000 planks. How big would it be? [About 120 feet in diameter.]

  6. You can reinforce this principle by drawing a 12” diameter circle on the blackboard, then a larger and larger circle, until only a part of the circle will fit on your board. As the circles continue to get larger, the portion of the circle you draw on the board will become straighter and straighter.

  7. Now imagine a circle as large as the Earth. [This would require 341 million KEVA planks.] From where we are standing, the circle would appear to be flat, but the Earth is round.

KEVA CHALLENGE: Construct a circle with a perimeter of 200 planks on a gym floor. [Almost 24 feet in diameter.]



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