Plane Figures: Horizontal line - curved or straight?

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  • A globe
  • Frame of smallest circle inset
  • Knitting needle



  1. Invite the child to identify their hometown on the globe.
  2. Place the inset frame on the globe so that the town coincides with the center of the circle.
  3. This curve (the rim of the frame) represents the horizon for everyone living here in and around the town.
  4. Because we are standing outside the earth we see the entire horizon as a circle, instead of as an arc-part of the circumference.
  5. With the chalk mark a point on the floor.
  6. Draw a circle around this center point.
  7. Invite the child to stand at the center.
  8. What do you see? Without turning the child can only see an arc, a part of the circumference.
  9. Reinforce the facts that in these demonstrations the child is much bigger than the circle on the globe or on the floor, when in reality it is the reverse.
  10. The child is a tiny, tiny point in relation to the earth which is huge.
  11. The curvature of that arc would be so slight that you would only be able to see a straight line.
  12. With the knitting needle, hold it so that it forms an arc on a horizontal plane.
  13. Invite the child to identify what he sees as he lowers his body..... a curved line.... a curved line... a straight line.
  14. At eye level this curved line looks like a straight line.

Control Of Error

Points Of Interest