Not suggesting that Newtonian Physics (for all the things it fails to explain) isn't good enough for everything we have done so far (and by definition better than the flat-earth crap).
However, more than 3 dimensions are required in the mathematics that 'might' explain a number of phenomena ...
I was suggesting that the average flat-earther is a moron (taking the guy in OP's clip who made the "upside down planes" comment as average) with an undeveloped understanding of relative perspective.
But I was also pointing out that the average non-moron's understanding of space is massively...
You can't.... flat or not.
There is an experiment you can do with small children to gauge when they first develop an understanding of *relative* position. You have a diorama of a landscape with various landmarks. You stand child at one side and place teddy bear/doll/action man somewhere else...