To show the “constructive power” (or analyzing power) of the triangle by exploring all possible shapes using only two triangles.
Preparation for geometry: to show that all plane figures constructed with straight lines are composed of triangles.
Preparation for understanding the concept of equivalence and its application for finding the area of plane figures.
4 to 5 years
- All the materials are blue with no black lines
- The number of triangles is reduced to the following:
A pair of equilateral triangles
A pair of isosceles right-angled triangles
A pair of scalene right-angled triangles
A smaller scalene right-angled triangle
A scalene obtuse-angled triangle
Invite the child by telling him you have something to show him. Bring him over to the correct shelves. Show the child how to carry the box. Have him carry it to the table and have him place it near the top right corner of the table. Have the child sit to your left, and then you sit down.
- Leave the shapes up above and remove the other triangles from the box.
- Remove the lid of the box using both hands.
- Place the lid directly in front of the box and place the box on top of the lid.
- Take out all of the triangles and place them randomly to the left of the box.
- Move the box above the lid and then replace the lid on the box.
- Place two of the same triangles together.
- Tell the child, “ Lets try and make new figures using these two triangles.”
- Hold one of the triangles still with your left hand.
- Place your right hand flat on the other triangle and slowly slide this triangle up along the edge of the other until their two points meet.
- Rotate the second triangle along this new edge of the first triangle until the edges are lined up.
- Remove your hands to see what form you have just “created”.
- Name the shape you have just created.
- Place your hands as they were and re-slide the second triangle back to its original position.
- Allow the child to try.
- Place that shape up in the top left corner and continue creating shapes with the other pairs of triangles.
- Always allow the child to try after each pair of triangles is “manipulated” by the directress. (Have the child name the shape he has created from the triangles.)
- Using the black lines as your guide once again, build the remaining shapes using the matching colors and line them up under the first three shapes.
The child works individually with the material as shown during the presentation.
The child works with the material but now the directress shows him the new figures that are made when one of the pairs is flipped over. The child can then explore these
As the child has been taught the names with the geometric cabinet, there is no language lesson given with this material.