also, i forgot a point

water is NOT flat. there is a thing called a "meniscus" and it's how plants pull water upwards. this effect is called "capillary action" and this is caused by surface tension in a container, the meniscus is concave, and when you fill a container to maximum, the water level can be slightly higher, and the meniscus is convex.

also, regarding straight lines and circles, there is a process called "normalization" where you zoom in on something. the more you zoom in on the edge of a circle, the more it looks like a straight line. at a certain scale, you would not be able to see it because it is under 0.1 degrees.

360 degrees is the path of a circle. the earth is approximately 10,000km from pole to pole, though the globe is slightly squashed due to centripetal force, the equator is something like 10500km or something like this.

human is max 2 metres tall, 10,000km is 10,000,000 metres, which means our perspective is of an arc of the CURVED surface which amounts to:

1/5,000,000 or one in five millionths is our height. the distance out to the horizon at sea level is approximately 5km. 5km is 5/10,000th or 0.005% of the CURVE of the earth.

at this level of scale, the surface of the sea is normalized to us. its curvature is less than an inch or two.

furthermore, if you ever saw a ship sailing over the horizon with a telescope, it would also appear to slowly be moving downwards as it continues on. like it does when the water is CURVED.

you really have to literally be IQ50 to believe this shit. not even 80 IQ people have trouble understanding these things if you draw them pictures and show them video.