We all have been witnessing growing propaganda from flat-Earth community. They are calling for common sense, claiming everything is clear and obvious, and we have been lied to for some odd reasons. Well, are they right? Should we be worried or  a scientific revolution is in progress in front of our eyes?
Their community is getting bigger and bigger every day, every day I see new YouTube videos with proofs of  flat-Earth, new articles everywhere. On the other hand, it's extremely rare to see some response to their claims. I tried to avoid such discussions as much as possible, because by paying  attention to such things you are giving them more importance, and that is counter-effective. But, these days, I was literally bullied by some flat-Earther, so I decided to write this article, and to explain why the Earth can't be flat using basic physics and simple reasoning. 

Center of mass

All isolated objects in the known Universe, ALL, tend to get spherical shape. Why? Every single object tend to be in the most stable physical configuration. That's why the atom is in ground state, if there is no any interactions, that's why an object won't move if you don't apply some force on it. Why is sphere the most stable? Because all points on its surface are experiencing the same force cause by internal gravity of the object. In other words, all surface points are on the same distance from the center of mass. On the other side, flat-Earth's center of mass can never be equally away from all surface points, thus  different surface points are experiencing different force, and because of that, flat-Earth, if it existed, would either evolve to sphere or fall apart.

Small Sun

So, the biggest issue of flat-Earth theory is if the Earth is really flat why do we see sunrise and sunset everyday, or why when in Australia is day, in Europe is night. If the Earth is flat then there is no need for time-zones, right? Flat-Earthers explain this by saying the Sun  is actually much smaller and closer than we think. In every flat-Earth video you can see this experiment, proving this claim. And that's ok. I'm not saying you can't prove day/night shift on flat-Earth, obviously you can.

And this is completely legit. But, amazing thing about science is that different disciplines are interconnected. So, when you are making a claim like this, you have to make sure that your theory is consistent with all other phenomenons it affects, not just with one you are referring to. For example, the Sun is producing energy we experience through radiation, in its core using thermonuclear reactions, such as fusion of hydrogen atoms. Conditions needed for fusion are extremely high pressure and temperature, and small Sun can't provide such conditions. There are lots of objects in the Universe that meant  to be stars but just didn't have proper dimensions and mass to provide needed conditions for nuclear fusion. And this is not conspiracy, just go outside and take a look at the Sun and you will feel the energy...

Flight paths

So, this is one of the main proofs for flat-Earth. Funny thing is that this is completely opposite, believe it or no, proof that the Earth is spherical. For example, planes flying from London to New York, are flying over Greenland, and this is illogical for flat-Earthers. This is illogical if you have in mind plane map of the Earth, because in plane geometry the shortest path between two points is straight line between them. But in reality we are working with spherical geometry, and here, the shortest path between two points is not straight line connecting these points, but the line of the great circle. Great circle is a circle on a sphere that goes through the center of the sphere. All other circles on a sphere, not containing the center of the sphere are just regular circles. Guess what, great circle, connecting London and New York goes over Greenland.

In this image above, you can see the illustration of a great circle, and an example, the shortest path between New Delhi and New York, on a sphere. You can obviously notice that the shortest path is not straight line between these two cities but a great circle line.

The Earth is stationary

Ok, flat-Earthers want to disprove that the Earth is moving by saying- why I can't feel this motion, why I don't feel  wind in my hair? 

The Earth is involved in different motions, it moves together with the Sun around the galaxy center at high velocity, but it also moves with the galaxy around something even bigger at even higher velocity. Lets make short elementary school experiment. Imagine a train moving at 500 km/h, and imagine yourself walking inside the train at 1 km/h. Observer standing outside of the train will notice that your speed is 501 km/h, but from your system of reference your velocity is just 1 km/h. If you are standing inside the train, you won't be aware of any movement, and consider yourself stationary. Now just replace the train with the Sun, and yourself with the Earth. So, the only movement Earth is experiencing is movement around the Sun and of course Earth's rotation.

But flat-Earther's next question is well, why can't I feel this motion? Let's repeat the same experiment, but now the train is the Earth, and the passenger represents us. Passenger inside the train can't feel any motion until the train is moving at constant velocity. The same thing is with the Earth, motion is at constant velocity. If Earth suddenly stopped, or suddenly increased or decreased its velocity we would feel it definitely, and it would be tough to survive.

Earth's rotation

Flat-Earther's argument is if the Earth is rotating and if I am somehow in the air (hovering in a helicopter in the same place) then due to Earth's rotation, ground would move beneath me, and eventually I would reach America, for example, not having to move at all! Interesting thing, this was Aristotle's argument in disproving Aristarchus' theory of Earths rotation. So, 2500 years later, we have the same misunderstanding of basic physical principles. At that time. Aristarchus' was not able to explain this, and his theory was rejected, just because he didn't know anything about inertia. Yes, inertia is the answer for this simple question. If you are not familiar with inertia, lets go back to the train. You are standing inside and not feeling any motion, but then train suddenly stops. Due to inertia your body  is going to move forward, regardless of your intentions.  That's what happens, if you are jumping in the same place and waiting for the Earth to move beneath you. You won't reach America but rather you would move together with the Earth, unwillingly.

There is of course, lots of other paradoxes involving flat-Earth theory, some of them are more complicated and require better understanding of physics, but these five explained here, using simple physics are completely enough to show how absurd is flat-Earth theory. Instead of trying to unsuccessfully change complete science, it's more convenient just to try to understand better concepts of center of mass, nuclear fusion, spherical geometry and inertia, and you will realize there is no need at all for changing anything so dramatically.