I met a guy who actually believed he had invented an automobile that would run on wind power - as in perpetual motion kind of thing. He reasoned that the wind from the car going forward would create the power to make the car go forward.
OK, we can forgive him for ignorance, but he confided that he had spent over $50,000 on parts that he had yet to assemble for a test model.
To humor him, I asked him what would happen if the car went downhill and gained so much speed from the additional wind that the car started to speed out of control. He had that one figured out - the car would have brakes. Ironically.... the last thing his design actually needs at this point is brakes...
