The world is flat.

I'm just going to approach the opponent's argument in the order delivered. I will label for clarity. Definition of FlatI don't contend my opponent's definition of flat, nor am I attempting to argue that the 3D objects cannot be flat. (While it is technically true that no surface can be perfectly flat due to small imperfections in the surface, this is a technicality that I do not need to use to prove my point.)Opponent R2 Claims.The Earth is a 3D object in the sense that it has length, width and height. I agree that the Earth is 3D and that it in some sense has a length width and height. However, since I'm arguing that the Earth is round, I believe terms along the lines of radius/circumference/etc. are a more valuable way of describing the Earth's shape. This argument is basically just showing that 3D objects can be flat on some/all sides, which is a reasonable claim in the context of this debate. A cube has squares on all sides. Yep. A square is a flat shape. Yep.A cube is flat.Not really. A cube isn't flat in and of itself, since it is a 3D shape. It does, however, have six flat sides. While I am able to accept a claim from the opponent that the Earth is like a plane of whatever shape with some thickness and that we should consider that flat, I am not willing to accept a claim that the Earth is a cube and that the entire cube should be considered flat. It has flat sides, yes -- but it is not wholly flat.Notice his definition 1b comes into play here -- in which is says that something would be "flat" if it had a relatively broad level surface in relation to thickness or depth. It cites a flat box as an example. A cube, by definition, is as wide as it is tall, so the definition of flat clearly does not apply.The world is a cube, which is flat.This does not follow from the previous arguments. While it is possible to imagine the Earth being the shape the opponent describes, this does not mean that the Earth is actually that shape. One could also imagine that the Earth is a sort of flat plate, that the Earth is a pyramid, that the Earth is a sphere, etc. You ability to imagine such a shape does nothing to prove the actual shape of the Earth. That would require evidence. Opponent's R2 Response to My ArgumentsWaterfalls at the end of the Earth, emptying the oceans. There are two issues with my opponent's response. The first is that he again claims the Earth is a cube, which I have demonstrated is not a flat object, based upon the opponent's own definitions. The second concerns the physics of an ocean on a cube planet. [1] Allow me to explain.Water always attempts to flow to the lowest point, due to gravity. As such, the oceans would be drawn toward the middle point of each face of the cube (in this cube world thought experiment.) This is because the distance from the core of Cube Earth to the points and edges of the cube is much greater than the distance to the midpoint of each face. The result of this would be 'bubble oceans' near the center of each face and no water near the edges of the cube. Ie, no waterfalls, since water would not flow over the edge of the cube. Since this whole argument came form the opponent's claim that he "saw a waterfall at the end of the ocean" in a movie (and if we ignore the obvious issues with using a movie as evidence), it is clear that the Earth the opponent saw in this movie could not be a cube shape. Thus, the opponent's Claim 3 from Round 1 defeats his R2 claim that the Earth is a cube. Also, see my point about how gravitational forces make Earth spherical in shape. Photographic EvidenceMy opponent actually brings up a good point here. I said that pictures were unreliable, as they are easily edited. However, I'd like to bring up the sheer wealth of pictures that have been taken from satellites. It would take a very long time to properly edit them so that each photo aligns with all previous photos taken. Additionally, different countries have taken these photos -- meaning for them to be fake there would need to exist an international conspiracy. There is no evidence that this is the case. Plus, there would not be a motive to edit these pictures in this way.Rather, it's easy to understand how a casual photo of a waterfall at the edge of the Earth could be manufactured. People are interested in what a waterfall at the edge of the Earth would look like, giving someone a motive to edit the picture to reflect this. Summary: While it's possible that all sat pictures of the Earth have been edited to hide the actual shape of the Earth, it is so unlikely that it need not be considered.Maps never reveal an edge.Maps are often not to scale because the Earth is spherical and because humans like to use rectangular sheets of paper. Changing the scale of the map (and stretching it at points near the poles) is the only way to actually fit the map on a piece of paper. Additionally, I mentioned that satellites have completely documented all regions of the Earth (in low detail) and there was no evidence of an edge, thus implying that one does not exist. The opponent dismisses this by stating that this is a conspiracy by the elite to trick the majority, but offers no evidence of this. Significant claims require significant evidence. The scientific reason the Earth is a sphereThe first part of the opponent's argument basically just says that "science has its limits" and that scientists are currently questioning the theory of relativity. Both statements are true, but they are irrelevant to my claim. We currently do understand the effects of gravity, even if we don't understand what causes gravity. The effects of gravity are actually so well understood that they are taught to first year physics students. This is not "edge science". His next claim is that it would take a very long for gravity to compress Earth into a sphere. This is also true. It's worth noting that the Earth is approximately 4 billion years old, which is more than a very long time. As for the evidence behind my claim: [2]Shadows on the moonThe opponent says that aliens are responsible, but does not present any evidence suggesting this is true. Significant claims require significant evidence. Ships leaving the portIt is possible that a ship might sink upon leaving shore, meaning the reason for it appearing to sink into the ocean is that it's literally sinking. However, it was noticed long ago that the same ships that sunk over the horizon also returned, ship intact and thoroughly unsunk. If the Earth were even only 'relatively flat' this phenomenon would not occur with all ships leaving port, which we know it currently does. CircumnavigationAgain the opponent brings up the cube idea, which I've thoroughly defeated. Also, planes don't defy gravity. It is well understood how planes remain airborne. ConclusionI have defeated the opponent's claims and defended my own. What I find odd is that on some points the opponent makes a reasonable attempt produce an effective argument and at other times makes an obviously ridiculous claim. (See: aliens, conspiracy theory)I suggest choosing one mode of attack and sticking with it. Either be serious or silly, but not both.Sources:(1) - http://www.askamathematician.com... (2) - http://www.universetoday.com...