I remember when I was 11 years old. I designed and built a model boat out of balsa wood. It had a big funnel arrangement on the top. I figured that if I gave it a good push, the air would get compressed through the funnel and come out the back in a jet that would push the boat forward so that more air would get compressed and keep the jet going. I can remember ceremoniously carrying it down to the pond in the park with my friends. I've been living off the earnings of my invention ever since.