Mejor en vez de pensar realizamos un experimento con un tanque de agua de 6 pies de altura, en una habitación a temperatura uniforme, dejando el agua en reposo durante 24 horas. Experimento realizado por Ascher Shapiro experto en dinámica de fluidos. El experimento salió bien pero la conclusión es que el agua debía estar al menos 24 horas en reposo (una rotación). Más o menos nos da y nos quita la razón a todos.
"Coriolis rotation can conceivably play a role on scales as small as a bathtub. It is a commonly held myth that the every-day rotation of a bathtub or toilet vortex is due to whether one is in the northern or southern hemisphere. An article in Nature, by Ascher Shapiro, describes an experiment in which all other forces to the system are removed by filling a 6 ft. tank with water and allowing it to settle for 24 hrs (to remove any internal velocity), in a room where the temperature has stabilized (temperature differences in the room can introduce forces inside the fluid). The drain plug is then very slowly removed, and tiny pieces of floating wood are used to observe rotation. During the first 12 to 15 mins, no rotation is observed. Then, a vortex appears and consistently begins to rotate in a counter-clockwise direction (the experiment was performed in the Northern hemisphere, in Boston, MA). This is repeated and the results averaged to make sure the effect is real. The Coriolis effect does indeed play a role in vortex rotation for draining liquids that have come to rest for a long time. ["Bath-Tub Vortex", Nature. Dec 15th, 1962. Vol 195, No. 4859, p. 1080-1081] [26]
In reality, this experiment shows that the Coriolis effect is a few orders of magnitude smaller than various random influences on drain direction, such as the geometry of the container and the direction in which water was initially added to it. In the above experiment, if the water settles for 2 hrs or less (instead of 24), then the vortex can be seen to rotate in either direction. Most toilets flush in only one direction, because the toilet water flows into the bowl at an angle.[27] If water shot into the basin from the opposite direction, the water would spin in the opposite direction.[28]