Long time lurker, first time poster, one comment here needs some clarification.
WOFanatic wrote:(I'm hoping nobody has said this yet). My favorite is the myth known as centrifugal force. It's a completely fictitious force, and it still boggles my mind that parks still use it for marketing purposes.
Centrifugal force isn't a myth, it's a perfectly valid force. I imagine your interpretation of the word "fictitious" is tripping you up, you have to think outside Newton's Laws to understand it.
Newton's Second Law says F = ma, if you don't have acceleration you don't have force. But have you ridden in a car around a corner and been thrown to the outside of the car while traveling at a constant speed? That makes no sense, F = ma says there's no acceleration so there's no force! And that's absolutely true, if you're using the standard inertial reference system used by Newton and traveling in a straight line. But if you use a rotating reference plane to account for the corner, rotating at an angular speed "ω" in degrees/second, you find there's an angular acceleration being produced by traveling around the corner. "Aha!" you may say, there's an acceleration which causes a force to be produced, and this is the centrifugal force that is supposedly "fictitious". If you really want to know the math the equation for centrifugal force is F = m*(ω^2)*r, hope that helps you understand why parks still refer to a perfectly valid force calculation when marketing rides.
I can't think of any myths/rumors that haven't already been said, some good ones have been posted here for sure.