Keep Telling Yourself: It's Only a Cartoon ...

I very rarely disagree with XKCD's cartoons, but this one baffled me. The explanation here doesn't help.Yes, I know, it's a cartoon, not a philosophical or scientific argument. But the cartoonist is very serious about his math and his science. And so much here is wrong.I'm sure that gliding in a wingsuit like the one depicted is fun; I've fantasized about free flight myself, many times. But