The premise of this questions is driven by the popular belief that when flushed toilets water rotates counter clockwise looking from the top in northern hemisphere and clockwise in southern hemisphere. Ahem! Let’s answer this age old myth perhaps popularized by the junk science used in “The Simpsons” show. If you recall, in one of the episodes of the Simpsons show, Lisa (the smarty pants) convinces her idiot brother, Bart, that when toilets are flushed in northern hemisphere water tends to rotate counter clock wise as it exits where as people in southern hemisphere notice that the water rotates clockwise due to effect of Coriolis forces. Bart never finds out answer to this dilemma even after spending an exorbitant amount of money on a collect call to Australia (Southern hemisphere).
Before we answer this question, let’s take a brief look at Coriolis force. Coriolis force also referred to as Coriolis Effect that comes into play due to the spherical nature of earth. Earth at its equator tends to rotate at a faster speed (due to bigger diameter) as compared to at poles (due to smaller diameter). So, if you observe an object moving from equator towards North Pole, it can appear to shift slightly towards right due to greater momentum at the equator, similarly this appears to veer left if moving towards South Pole.
People also compare that tornado directions in southern hemisphere tend to spin clockwise as compared to counter clockwise in northern hemisphere. While Coriolis Effect may play small role in tornadoes, it is not great enough to truly influence the rotation direction. Tornadoes have been observed to rotate in both directions i.e. clockwise as well as counter clockwise in northern hemisphere as well as southern hemisphere.
Coriolis Effect is not strong enough to influence the drain direction of the toilet or sink water. The toilet water direction is more a function of the design of the toilet bowl angle and the location of the nozzle and direction of the spray. You may see the clockwise rotation of toilet water when you are in Brazil (southern hemisphere) be assured that it is NOT due to Coriolis Effect, but due to the design of the toilet bowl itself.
While the Coriolis Effect may not have any impact on the toilets water rotation direction but it certainly impacts the weather patterns. When you are watching the weather channel or the weather forecast on TV, all the small arrows that are displayed on the meteorological map indicate the direction of the wind. The direction of the wind is driven by Coriolis Effect.
So the next time you want to impress your friends and someone spring this question don’t hesitate to say that Coriolis effect has no impact on the direction of the water flow in the toilet bowls in northern hemisphere vs. southern hemisphere and put the controversy to rest.
