| Purpose: |
To estimate inaccessible
distances using the principle of an isosceles right
triangle. |
| Season: |
All |
| Materials: |
Silva compass Paper, Pencil
Wooden stakes, Hammer |
| Description: |
Compasses are used to
establish an isosceles right triangle over an
inaccessible distance (or a simulated one). (Refer to 3rd
grade Miller Springs curriculum, "Lost and Found, to
learn how to determine a bearing.) The length of the
accessible side of the isosceles right triangle is
measured in order to estimate the inaccessible side.
Thus, two sides of the isosceles right triangle are equal
in length and the two angles formed by the sides and the
hypotenuse are 45 degrees. |
| Procedure: |
- Discuss with students the characteristics of an
isosceles right triangle. Mark off several
distances on the playground with wooden stakes or
markers and have small groups of students
estimate these distances using the following
steps:
- 1. Use the compass to determine bearing
from Point A to Point B on opposite bank
of a river (or points designated on the
playground).
- 2. Find bearing from Point A to Point B
(degrees is used in the example).
- 3. Take a new reading from A by
subtracting 90 degrees to form line x (if
bearing from A to B is 180 degrees, line
x is in the direction of 90 degrees).
- 4. Move along line x to a point C where
the bearing from point C to point B is
225 degrees (180 degrees + 45 degrees).
This forms an isosceles right triangle
ABC with sides AB=AC.
- 5. Pace off distance between Point A and
Point C to determine the width of the
stream at AB.
- Have students check answers with the actual
measurements. You may want to plan a field trip
to a location where this technique can actually
be applied. Compare this technique with the Brim
of the Hat method.
|
| Extensions: |
Invite a surveyor to visit
the class, demonstrate the equipment, and explain
techniques used to determine inaccessible distances. |