Find the lost hunter.
1. Explain that the class has to locate a hunter lost in the woods
who is trying to relay information about his location by radio to his
rescuers. Ask for a volunteer to play the lost hunter.
2. Ask for a second volunteer to play the role of a mountain.
Position the mountain about 10 feet from the lost hunter. Assume that
the lost hunter can only see the mountain.
3. Ask for a group of students to play the roles of the "Search
and Rescue Team." They ask the hunter to describe his position to
them. (Probable answer: "I can only see a mountain.")
(The Team may find it easier to put a symbol for the mountain on a
piece of paper and discuss where the hunter might be in relation to the
mountain on the map.)
Will this information help the Search and Rescue Team?
4. Add a second landmark (another volunteer): a television
transmission tower. Position the TV tower about 8 feet away from the
lost hunter, so that the hunter, TV tower, and mountain form a triangle.
5. The lost hunter now has two points of reference for the Search
and Rescue Team when asked to describe his location. (as, "I see a
mountain off to my right, a TV tower to my left.").
Is the Team able to narrow down his location better?
6. Add a third point of reference: a giant redwood tree 6 feet away
from the hunter, so that the mountain, TV tower, and redwood tree form a
triangle around the lost hunter.
7. Now have the Team ask the hunter for his probable location. ("I
can see a mountain to my right, a TV tower ahead and to the left, and a
giant redwood tree behind me.")
Using 3 points, the Team can now triangulate the position of the
8. Explain to students that this is how GPS (Global Positioning
System) works. Instead of mountains, TV towers, and other landmarks, it
uses highly-accurate satellites as points of reference. Instead of
relying on vision to estimate one's location and distance, handheld
satellite receivers communicate constantly with the orbiting satellites,
triangulating on at least three of them. This enables the receiver to
display one's position to within 100 meters.