Origin of myth
there is an myth out there that states that "the water always goes down the drain” and goes further: “According to the hemisphere in which the sink is located, the direction of rotation of the water is different”. The myth that water goes down in direction anti-schedule at the hemispheresouth and in the senseschedule at the hemispherenorth has even been aired in magazines in disclosurescientific is on Software in television.
It is certainly not known when the myth arose, but it is sustained by the existence of a well-formed scientific concept capable of explaining the direction of rotation of the cyclones and the air masses of the atmosphere. However, this idea takes into account the existence of a non-inertial force call of strengthinCoriolis. Gustave-Gaspard Coriolis (1792-1843), a French mechanical engineer and mathematician, was the first to describe how this strengthfictional Act.
Coriolis force
THE strengthinCoriolis only appears in referentialnon-inertial, that is, accelerated. The Earth, for example, is in constant motion of
rotation around its own axis and therefore has a centripetal resultant of acceleration.To understand this force, just imagine that if a body moves straightly at high speed with respect to Earth or for a long time, the trajectory of this body in relationship to the ground (which also moved) noit will be one more linestraight.
This force is always perpendicular the direction of velocity of bodies relative to the Earth (or whatever the frame of reference, as long as it is rotating). On Earth, this acceleration cannot exceed values of 1.5.10-4 x V m/s2, being V the speed of the body relative to the Earth's surface.
THE accelerationproduced by the force of Coriolis is very small compared to the acceleration produced by Earth's gravity and will only produce some observable effect on bodies that move a lot rapidly, in the order of hundreds of meters per second (as in the case of projectiles and rockets), in air masses moving at tens of meters per second (causing the cyclones) or even in bodies that move for very long intervals of time.
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Assuming that the velocity of the water that goes down the drains all over the world is of the order of just a few centimeters per second, even in the most distant positions from the Equator – at the poles, where we would have the maximum values for the forcesinCoriolis, the accelerations produced would not exceed 1.5.10-6 m/s2, millions of times smaller than the acceleration of the Earth's average gravity, of the order of 9.8 m/s2.
Why is this theory wrong?
To test this intriguing phenomenon, the professor of mechanical engineering at MIT (Massachusetts Institute of Technology), AscherShapiro, carried out a series of water runoff experiments, leaving it in rest during periods of up to 24h and withoutcontact with the air. After that time, the water went down in a vortex (swirl), but with speedsmuchminors than when poured directly over the sink with the drain open.
Your conclusions pointed out that, even after all this time, there was still timeangular remaining between the water masses, and this affected the conditionsinitials of the experiment. Furthermore, these conditions were mainly responsible for the direction of rotation of the water during its flow, as well as the shape of the sink, which affects the conditions of movement.
If you're still not convinced, try throwing the water down a drain initially in the senseschedule and then in the anti-schedule. If Shapiro is wrong, when water is released clockwise in the southern hemisphere, it may slow down and reverse its direction of rotation.
By Rafael Hellerbrock
Graduated in Physics
Would you like to reference this text in a school or academic work? Look:
HELERBROCK, Rafael. "The Myth That Goes Down the Drain: The Water That Goes Down the Sink Does Not Depend on the Earth's Hemisphere"; Brazil School. Available in: https://brasilescola.uol.com.br/fisica/o-mito-que-desceu-pelo-ralo-agua-que-desce-pela-pia-nao-depende.htm. Accessed on June 27, 2021.
