Here is a video I found by accident of someone putting water on a spinning ball and filming it at high speed to see what it looks like. This will make an excellent flat earth experiment. This is what happens when the ball is spun by hand (a couple of miles per hour at the most). Now, tell your friend what it would be if it was at 1,000mph. Gravity or no gravity no way can water stay in a spinning ball at 1,000mph!