A Teacher's Journal: Experimenting with Crazy Cars
Nancy C. Whitman · Teaching Children Mathematics · 2000
The activity described in this article will help students confirm the fact that the sum of the measures of the interior angles of a triangle is 180 degrees. The idea for the activity occurred to me when a student explained how she “proved” this fact to herself. She said, “The way a pencil points after it moves in all the inside angles is opposite from what it was at the start.” Her explanation is represented in figure 1. For such an explanation to be meaningful, students must understand that if an object is turned so that it faces in the opposite direction, it has rotated 180 degrees. Teachers must make sure that students have acquired this knowledge before the start of the activity. Teachers can help students make this discovery by having them rotate their pencils in known angle increments until the pencil points in the opposite direction. At the start of the activity, students should discuss what they know of “crazy cars,” or “bumper cars,” and the kinds of experiences that they have had with such cars at carnivals. You should ask students about the shape of the arena or track in which the cars are driven and discuss possible reasons that the track takes a particular shape. Emphasize that in addition to going forward and backward, the cars also rotate when they hit the sides of the track.