Here is a joke that I read in a cartoon in magazine a while back. I can only paraphrase and the animation is helpful too, but:

Lt. Green was out on his first solo flight in a T-38 and was feeling a bit cocky. He decided to see what ballistic flight was like and pulled the jet into a vertical climb. After a few seconds he got a call from the tower as follows, "Ghost 53Z, tower. Say heading," to which the pilot responded "Uh, up, sir."