Plane Figures: Parts of a Straight Line

Age

6-9.

Materials

• Two strings attached to spools
• Two scissors
• A red felt pen.
  

Presentation

1. Again the directress prepares the spools in her hands and invites the child to watch as the line appears.
2. What is it? A line...a straight line... a straight line....
3. Invite the child to find a point on this straight line and mark it in red.
4. The child then takes the scissors to cut the line at the point... this is a straight line... (cut).
5. Taking one spool and the point, the teacher extends the string... this is a ray... this is a ray.
6. The directress identifies the other ray in the same manner.
7. These two rays are equal. a ray starts from a point and goes on to infinity.
8. This red point is the origin.
9. Therefore a point divides a straight line into two rays.
10. With the other spool the situation is repeated, with child identifying a straight line.
11. This time the child is invited to make two red points on the line, and to cut the line at the two points simultaneously.
12. Before the cut, the line is identified as a straight line.
13. After the cut the directress takes on piece at a time.
14. This is a ray. This is another ray.
15. This is a line segment.
16. The two red points on this line segment are called endpoints, because we can't tell which is the beginning and which is the end.
17. Therefore two points divide a line into two rays and a line segment.
    

Variation

Classified nomenclature - after the child has put the cards with the corresponding labels, have him put them in order: origin, ray, endpoints, line segment.