File this under, "Sometimes we know more than we can prove". Yes Virginia, a curveball does curve. I can't believe that this is still a question in some minds.
Science Or Myth? Breaking Curveballs In Baseball:
"Baseball players will tell you that a fastball can rise - and elementary physics says it can also, the same way an airplane rises because the teardrop shape of a wing causes air to go over the top faster than below the flatter bottom, 'sucking' it into the air. Sure, if the baseball is going 200 MPH it can happen. But they don't.
Likewise, curveballs can break sharply, some say, while others disagree, including us a year ago (see Does A Curveball In Baseball Really Break?). It's an illusion. Still a K if you miss them often enough, though, so players are forgiven if they are convinced they got beat by science."
'via Blog this'