They don’t “say” the earth is rotating, we know it is, because people have literally watched it happen in front of their eyes while in orbit. But before we ever sent anyone to space, we were already very good at determining the shape of our planet and the dynamics of our solar system just by making observations from the ground. Ever notice that the stars aren’t always in exactly the same spot when you look up? That’s because the earth rotates and orbits around the sun.

Airplanes do not fly in a straight line, it just looks like they do if you look at their flight path from above. Kind of like how the earth might look flat if you only look at a paper map. It’s not.

It’s hard to tell if this post was a joke, troll, or a genuine question by a young student who hasn’t taken any science or geometry classes yet, which would be totally fine. But these are concepts that we’ve had a very clear understanding of for a very long time. Pick up nearly any astronomy book and you’ll have your answers.