A Glass of Water

The surface of the water in a glass of water is practically flat. Some flat-Earthers claim this is ‘evidence’ that the surface of the water is flat, and it will always be flat no matter how wide the container. They are wrong.

If the Earth is a sphere with the radius of 6371 km (3960 miles), then the surface of the water in a 10 cm (4 in) wide glass will have a bulge of 0.00000002 cm as the result of gravity, excluding other effects like the surface tension.

To put it into perspective, 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 would like 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—, then a mere visual observation is certainly not acceptable.

The fact that the surface in a glass of water appears flat definitely matches the expectations in the spherical Earth model.

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