Consider a sphere. Since a sphere has a consistent shape, no matter where on it you stand, you have exactly the same amount of sphere under you. (Imagine an ant walking around on a crystal ball. From the insect's point of view, the only indication of movement would be the fact the ant is moving its feet—the shape of the surface would not change at all.) A sphere's center of mass is in the center of the sphere, which means gravity will pull anything on the surface of the sphere straight down toward the center of the sphere. This will occur no matter where on the surface the object is located.
 3) The natural physics of water is to find and maintain its level. If Earth were a giant sphere tilted, wobbling and hurdling through infinite space then truly flat, consistently level surfaces would not exist here. But since Earth is in fact an extended flat plane, this fundamental physical property of fluids finding and remaining level is consistent with experience and common sense.
The Earth is different from other planets, that much is true. After all, we have life, and we haven’t found any other planets with life (yet). However, there are certain characteristics all planets have, and it will be quite logical to assume that if all planets behave a certain way, or show certain characteristics—specifically if those planets are in different places or were created under different circumstances—our planet is the same.

60) Anyone can prove the sea-horizon perfectly straight and the entire Earth perfectly flat using nothing more than a level, tripods and a wooden plank. At any altitude above sea-level, simply fix a 6-12 foot long, smooth, leveled board edgewise upon tripods and observe the skyline from eye-level behind it. The distant horizon will always align perfectly parallel with the upper edge of the board. Furthermore, if you move in a half-circle from one end of the board to the other whilst observing the skyline over the upper edge, you will be able to trace a clear, flat 10-20 miles depending on your altitude. This would be impossible if the Earth were a globe 25,000 miles in circumference; the horizon would align over the center of the board but then gradually, noticeably decline towards the extremities. Just ten miles on each side would necessitate an easily visible curvature of 66.6 feet from each end to the center.

180) The spinning ball model dictates that the Earth and atmosphere would be moving together at approximately 500mph at the mid-latitudes where an LA to NYC flight takes place. The average commercial airliner traveling 500mph takes 5.5 hours traveling East with the alleged rotation of the Earth, so the return flight West should take only 2.75 hours, but in fact we find the average NYC to LA flight takes 6 hours, a flight time totally inconsistent with the spinning ball model.
77.) "Oh, but if the Earth is a plane, we could go to the edge and tumble over!" is a very common assertion. This is a conclusion that is formed too hastily, and facts overthrow it. The Earth certainly is, what man by his observation finds it to be, and what Mr. Proctor himself says it "seems" to be. flat – and we cannot cross the icy barrier which surrounds it. This is a complete answer to the objection, and, of course, a proof that Earth is not a globe.
25.) The surveyor's plans in relation to the laying of the first Atlantic Telegraph cable, show that in 1665 miles – from Valentia, Ireland, to St . John's, Newfoundland – the surface of the Atlantic Ocean is a LEVEL surface – not the astronomers' "level," either! The authoritative drawings, published at the time, are a standing evidence of the fact, and form a practical proof that Earth is not a globe.