They discuss not only the form of the position function itself, but also the speed with which the car moves, how it looks and sounds at different points in the motion, even how their predicted motions felt when they moved the blue car. Next Ms. Johnstone asks a student volunteer to draw a graph on the computer that remains hidden from the class. She assigns the red car to move according to the graph, and, still keeping the graph hidden, asks the students to guess from watching the car's motion what the graph looks like. She replays the motion several times, while students discuss and implement various schemes to measure and describe the car motion. Finally, Ms. Johnstone asks the class to use their graphing calculators to sketch the graph of the red car's motion.
Several students take their turns, downloading their graphs from their calculators to the blue car.
The class watches the blue car move first, and assesses how close its motion is to the red car's motion. Then Ms. Johnstone runs both cars together, and students compare the two motions, and suggest changes in the blue graph to make the two motions more similar. Finally, Ms. Johnstone shows the graph to the class. The student who drew it explains why it caused the red car to move in the way it did, and explains differences between his graph and the ones other students made. Other students and Ms. Johnstone contribute to his explanation.