A lot of this stuff is mysteriously absent from the FAQ. So....
Many spacecraft have photographed pictures of the Earth and it is indeed, a sphere. How can this evidence be wrong?
FE claims these photos are doctored as part of a worldwide government conspiracy to hide the truth.
When travelling in a straight direction, you will always reach the same point on the globe from where you started. How can this happen if the world is flat?
Your statement is based on the assumption that the Earth is, in fact, a globe. If it isn't, then it won't be the case that what you predict would occur. So, have you taken a large number of trips, yourself, in straight lines around the world and reached the starting point?
If the world was really flat, what would happen if you jump off the disc's edge?
You would enter an inertial reference frame, moving at a constant velocity in the direction the Earth was moving before you jumped. The Earth would continue accelerating upwards past you at a rate of 1g, so it would appear to you that you were falling into space.
The Earth is like any other planet.
Another assumption...
Scientists have confirmend this.
How have they done this? Was it using techniques you could replicate yourself? Reproduction of results is a very important tool in science, but somewhat lacking in planetology. Also, first-hand measurements tend to rare.
On the other hand, it's safe, I think, to assume that the Earth is just like itself, and consequently, just like bits of it that you may take out (only bigger, and more varied). As it turns out, you can demonstrate a gravitational attraction between bits of the Earth that you take out of the Earth, and you can do it in the comfort of your own home. Google for "torsion balance experiment" (by Cavendish, IIRC).
If the Earth was indeed a flat disc, wouldn't the whole planet crunch up into itself and eventually transform into a ball?
If the Earth generated a gravitational field, yes, it would *eventually* happen, after a billion years maybe. FE assumes that the Earth does not generate a gravitational field. Also, I'm not sure what FE's stance on the age of the world is, but it's plausible that it's a younger estimation than the RE claim.
How come you can see the Earth's natural curve from very high altitudes? Such as planes and the summits of various mountains?
Are you talking about the curve of the horizon? How can you tell the difference between the curve caused by standing on a spherical ball, and the curve caused by standing on a circular disc? To me, in both cases, the horizon should appear circular. The circles would have different curvatures, certainly, but how are you sure you are seeing one and not the other?
The relevant curve for demonstrating the Earth to be ball-shaped is the curve away from you, not the curve around you. The flat Earth has a curved edge, so of course it will appear curved. However, it does not curve down and away, the way the top of a hill or an upside-down salad bowl do.
How would a disc-shaped planet survive under the harsh environment of space?
How does the ball-shaped planet do it?
Wouldn't it collapse or be unable to sustain an atmosphere?
Collapse? See above. Atmosphere? There's a gravitational effect; it, along with the ice wall, holds some atmosphere in.
What lies underneath a flat Earth? Is it the sun or the moon?
That's in the FAQ; in answer to your second question, no; they are above the plane in which the flat Earth lies.
Why do planes and ships slip through a horizon instead of shrinking smaller and smaller?
No explanation is given, aside from gibberish that you can and should ignore.
If the Earth was flat, we would be able to see the coastland of China from America by using a powerful telescope.
If it were flat and there were no atmosphere, that would be true. However, the resolving power of a telescope is limited by scattering from the atmosphere. Also, light attenuates faster in the atmosphere than in vacuum.
Who knows? I might even become a Flat-Earther too someday!
[sarcasm]We can only hope...[/sarcasm]
-Erasmus