Flatness refers to the shape of a liquid's free surface. On planet Earth, the flatness of a liquid is a function of the curvature of the Earth, and from trigonometry, can be found to deviate from true flatness by approximately 19.6 nanometers over an area of 1 square meter, a deviation which is dominated by the effects of surface tension. This calculation using the Earth's mean radius at sea level, however a liquid will be slightly flatter at the poles.


This article uses material from the Wikipedia article Flatness (liquids), which is released under the Creative Commons Attribution-Share-Alike License 3.0.