It's been surmised by flat-earthers that if the Earth is moving then we should be able to lift off of the ground in a balloon and the ground should travel below us. Others have suggested that flights going with the rotation of the globe should be impossible because the globe rotates at 1000 mph but planes only fly at about 500 mph. These theories are both part of the same false premise which is that as soon as we leave the ground we should cease to travel in the same direction and speed as the Earth.
It's hard to believe some of the silly demonstrations thought up to prove the Earth is flat. One recent demonstration that has been filmed by a number of guys is bringing a spirit level (bubble level) on a plane and looking for the device to show the nose of the plane pointing down. Roll your eyes all you want, but this is a real test that some people take seriously. Below I will describe exactly why this test won't work.
I've heard from a number of flat-earthers that the spinning globe doesn't make sense because the objects would fly off of it. Just like a merry-go-round, the spinning creates a centrifugal force. They usually follow that up with irreverent numbers like the fact that the Earth has a rotational speed of around 1000 mph. But they fail to understand that linear distance traveled is not related to centrifugal force. Example video below.
If you talk to enough flat-earthers you will discover that two theories dominate the gravity discussion. The first theory is Universal Acceleration which has already been discussed by WTC. The second theory is less developed but claims that gravity does not exist and that objects rise and fall because of density. This density theory is what this post is about.
At this time (2019) flat Earth theorists have devised two wide-spread theories about what causes "gravity", or at least what causes the effect that we call gravity. The first theory, which is fading among the older flat-earthers, is that the flat earth is accelerating upwards which causes a downward force on the surface of the earth. The second is density theory. We will address universal acceleration in this post.