Plane Figures: Horizontal line - curved or straight?

Age
6-9.

Materials

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

Presentation

 * 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.