Parabola - Folding Activity
Latest update to this document: 26 February 2003


Hands on Activity:

  1. Mark bottom edge of paper with solid color (black)
  2. Make a dot (point F) 1"above the center of the lower edge of the paper.
  3. Fold the black line up so that it touches the dot. Make a sharp crease. Open the paper flat.
  4. Fold again in a different direction. Again make sure the black line touches the dot. Crease and open flat.
  5. Repeat about 20 times, folding the paper in a different direction each time. The black line must always touch the dot.
  6. Lightly trace the curve that appears.
  7. This curve is called a parabola.
    Definition - A parabola is the set of all points in a plane equidistant from a fixed point (called the focus) and a fixed line (called the directrix). (The directrix is the black line)
  8. Mark a random point on the parabola (point B), using the ruler draw a line from that point B to point F. Label the line K.
  9. Fold paper again so that the crease of the paper goes through point B while the edge of the paper touches point F. You should see line K through wax paper, trace the line. Label it, line L. This should form a perpendicular line with the lower edge of the paper through point B.
  10. Unfold the paper, you can see line segments L and K are the same length. (Thus proving that the distance from the focus to the point is equidistant to the distance from the point to the directrix.

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