Cars on Tracks
We learned about the types of friction involved with rolling cars, and ways that friction is decreased on real wheels, axles, and cars. The first week one we built cars using K'Nex components. We discovered that heavier, but not too heavy cars, shorter cars, and those with larger wheels tended to travel farther. The car that traveled the farthest, nearly 10 meters, was "Speeder". The creators of this vehicle balanced the wheels using different numbers of washers on the wheels so that it traveled straight, not bumping into the guide rails.
The second week we designed and built cars using Thames and Kosmos components. The wheels turned on fixed axles in the K'nex cars; the wheels are fixed while the axles turn on Thames and Kosmos cars. Several cars hit the wall at about seven meters. Some designers discovered what happened when the center of gravity was too high!
Students took turns doing experiments with a four-track device. The first investigated whether the path a ball took rolling from the top of the track to the bottom made a difference in the ball's final speed. (It didn't.) the second answered the question of whether the mass, weight, of the ball determined its final speed. It didn't, unless the ball was so light (a ping pong ball) that air resistance made a difference.