You're looking up at the sky and you see lights moving in that sky. You do not feel any motion to say it's you moving on a sphere but you are simply told, you are.
We've had this drummed into us from being a kid, so I have no issue with anyone going with that flow. I simply used to but absolutely do not for reasons I've given which you have every right to argue.
That doesn't address the issue I described to you, of the specific paths the "lights" take across the sky while you're observing them.
I.E if you're near the middle of your disc model in the UK, Europe, Asia or the US, the lights APPEAR to be rotating ANTI-CLOCKWISE around a polar point in the sky.
Whereas if you're further away from the middle of your disc model in Australia, South Africa, or Argentina, you see a completely different set of lights rotating CLOCKWISE instead, again around a polar point in the sky.
And if you're halfway in between the middle and the outer rim, the lights instead make a STRAIGHT path across the sky.
If you travel from one of these "near the middle" countries to one of the "halfway" countries and on down to one of the "further away" countries, you can watch the transition from one pattern to the next to the next.
When you do this, it is clearly seamless, with no distortions like you might expect if there was a change in curvature of a lens or dome, and no moments where you can see one light turn into two as if reflected against something funnily shaped.
Curved mirrors / lenses / bowls-seen-from-the-inside
cannot achieve this effect without the use of magic to deceive the observer.
However if the planet is a sphere then the lights are doing EXACTLY what you would expect them to do.
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With regard to "not feeling the motion":
If you're sitting on a train travelling at a constant 150mph with the windows closed, and you throw a tennis ball directly up in the air, it will fall directly back down again in exactly the same way as if the train were not moving at all.
If you walk from the back of the train to the front of the train while it is travelling at constant speed, it takes no more effort than walking from the front of that same train to the back, and no more or less effort to walking in either direction when the train is stationary.
You cannot feel "constant motion" in a closed system.
Now, you
can feel acceleration and deceleration, and either of those
will affect the path of the tennis ball or your ability to walk from one end of the train to the other. But if the train is moving at a constant speed in a straight path then neither you or the tennis ball would be affected at all.
Water conforming to the container it is in and absolutely not conforming to a convex curve/ball is just one nailed on realistic proof. But like I say, those who are adamant the Earth is a supposed oblate spheroid, who are in the majority, are going to discard all of the evidence in favour of the magical mysteries that show a spinning ball in a so called vacuum of supposed space with nice pictures and video etc to just push it all home.
I can't compete with that but I can certainly not believe any of it.
I just leave it up to people to decide to question it, or not. It's not my call.
Water, like everything else, is subject to gravitational force and unless it is also acted upon by an additional net external force, it will fall towards the largest nearby mass, in our case, the planet itself.
If you take a glass of water and turn it upside down, the water will no longer conform to the shape of the glass, it will fall out onto the floor for the exact same reason that water will fail to conform to a small convex curve/ball when you conduct that experiment this close to the planet Earth.
Regardless of the shape of the container, the water always falls towards the centre of the large mass whose gravitational force is acting upon it. In the case of these two containers in our experiment, (the glass and the ball), the large mass towards which the water falls is the centre of the planet itself, and therefore obviously we observe the water conforming to the upright glass but falling off the ball towards the centre of the planet.
Now, if the curved container were suitably huge (say, a few hundred miles across, and curved in such a way that its curvature matched that of the planet) you would be able to see that the water
would conform to that shape, just like it does to the small glass or beaker in your home experiment.
Equally, if your
flat container were suitably huge (say, the same width as the curved one in my example above) then the water would no longer have the same depth all across the container, it would bulge in the middle, as if it were a gently-sloping perfectly curved hill of water, shallower at the edges, deeper in the middle.
Now, the container doesn't actually have to be that big for this experiment to work, as long as the curvature of the curved container matched the curvature of the planet. Because of the sheer size of the planet though, with the naked eye, a container small enough to hold in your hand that matched the earth's curvature would be barely distinguishable from a completely flat container, if at all.
So, while you are clearly correct that if you try the experiment at home, water will not conform to a small ball but will conform to a small flat container such as a glass or beaker, in actual fact this is only true if the curved container/ball has a curvature that doesn't match the curvature around the nearest source of gravity, which in our case is the planet itself.
Therefore for a fair test of "flat container versus curved container" for this experiment, you need to use a curved container whose curvature matches the curvature of the Earth, otherwise the experiment is flawed and the conclusion we are led to will be erroneous.
