Earth’s gravity causes water’s surface to curve with the same radius as Earth’s. On glass with a diameter of 10 cm, Earth’s gravity causes the water to form a curvature of 0.00000002 cm, outside other factors like surface tension.
Flat-Earthers like to demand that we prove water curvature in a glass of water. In reality, whatever the container, the curvature of the water surface remains the same as Earth’s radius. On a glass of water, it will be too small to observe.
The figure of 0.00000002 cm or 0.2 nanometer is smaller than the diameter of a water molecule (H₂0) which is about 0.275 nanometer. If any flat-Earther wants to prove the Earth is flat from a glass of water, they have to show there’s no such bulge. Because the bulge is minuscule, smaller than the diameter of a water molecule, a mere visual observation will not be sufficient.
The container’s shape and size do not affect the shape of the water surface. It still curves with the same radius as the Earth. As a result, the curvature is only visible on a large body of water—for example, a receding ship disappearing from its bottom first.
References
- Water Curvature – FlatEarth.ws
- What is the approximate size of a water molecule? How was it first measured? – Quora