by Nitpicker » Wed Feb 05, 2014 2:35 am
neufer wrote:
http://en.wikipedia.org/wiki/Coriolis_effect#Draining_in_bathtubs_and_toilets wrote:
<<Contrary to popular misconception, water rotation in home bathrooms under normal circumstances is not related to the Coriolis effect or to the rotation of the earth, and no consistent difference in rotation direction between toilets in the Northern and Southern Hemispheres can be observed. The formation of a vortex over the plug hole may be explained by the conservation of angular momentum: The radius of rotation decreases as water approaches the plug hole, so the rate of rotation increases, for the same reason that an ice skater's rate of spin increases as they pull their arms in. Any rotation around the plug hole that is initially present accelerates as water moves inward.
Only if the water is so still that the effective rotation rate of the earth is faster than that of the water relative to its container, and if externally applied torques (such as might be caused by flow over an uneven bottom surface) are small enough, the Coriolis effect may determine the direction of the vortex. Without such careful preparation, the Coriolis effect may be much smaller than various other influences on drain direction such as any residual rotation of the water and the geometry of the container. Despite this, the idea that toilets and bathtubs drain differently in the Northern and Southern Hemispheres has been popularized by several television programs and films, including "Escape Plan", Wedding Crashers, The Simpsons episode "Bart vs. Australia", and The X-Files episode "Die Hand
Di
e Verl
etzt". Several science broadcasts and publications, including at least one college-level physics textbook, have also stated this.
In 1908, the Austrian physicist Ottokar Tumlirz described careful and effective experiments which demonstrated the effect of the rotation of the Earth on the outflow of water through a central aperture. The subject was later popularized in a famous article in the journal Nature, which described an experiment in which all other forces to the system were removed by filling a 6 ft tank with 300 U.S. gal of water and allowing it to settle for 24 hours (to allow any movement due to filling the tank to die away), in a room where the temperature had stabilized. The drain plug was then very slowly removed, and tiny pieces of floating wood were used to observe rotation. During the first 12 to 15 minutes, no rotation was observed. Then, a vortex appeared and consistently began to rotate in a counter-clockwise direction (the experiment was performed in Boston, Massachusetts, in the Northern Hemisphere). This was repeated and the results averaged to make sure the effect was real. The report noted that the vortex rotated, "about 30,000 times faster than the effective rotation of the earth in 42° North (the experiment's location)". This shows that the small initial rotation due to the earth is amplified by gravitational draining and conservation of angular momentum to become a rapid vortex and may be observed under carefully controlled laboratory conditions.>>
That article is misleading, neufer. Obviously, there are ways to counteract the "natural" direction of the water spiral, or to stop it spiralling completely. Many sinks are too small to observe any spiral (without forcing one). And toilets in Australia typically have a lower water level than toilets of American design, so Australian toilets are much more turbulent and typically never spiral when flushed. But bathtubs are typically big enough to produce a spiral when draining, and statistically speaking, water draining from bathtubs in the Southern Hemisphere will have a slight tendency to spiral in the opposite direction, compared with the Northern Hemisphere. And again, statistically, bathtubs that are closer to the equator tend to take slightly longer to drain.
[quote="neufer"]
[quote=" http://en.wikipedia.org/wiki/Coriolis_effect#Draining_in_bathtubs_and_toilets"]
<<Contrary to popular misconception, water rotation in home bathrooms under normal circumstances is not related to the Coriolis effect or to the rotation of the earth, and no consistent difference in rotation direction between toilets in the Northern and Southern Hemispheres can be observed. The formation of a vortex over the plug hole may be explained by the conservation of angular momentum: The radius of rotation decreases as water approaches the plug hole, so the rate of rotation increases, for the same reason that an ice skater's rate of spin increases as they pull their arms in. Any rotation around the plug hole that is initially present accelerates as water moves inward.
Only if the water is so still that the effective rotation rate of the earth is faster than that of the water relative to its container, and if externally applied torques (such as might be caused by flow over an uneven bottom surface) are small enough, the Coriolis effect may determine the direction of the vortex. Without such careful preparation, the Coriolis effect may be much smaller than various other influences on drain direction such as any residual rotation of the water and the geometry of the container. Despite this, the idea that toilets and bathtubs drain differently in the Northern and Southern Hemispheres has been popularized by several television programs and films, including "Escape Plan", Wedding Crashers, The Simpsons episode "Bart vs. Australia", and The X-Files episode "Die Hand [b][color=#0000FF]D[/color][/b]i[b][color=#0000FF]e Ver[/color][/b]l[b][color=#0000FF]e[/color][/b]tzt". Several science broadcasts and publications, including at least one college-level physics textbook, have also stated this.
In 1908, the Austrian physicist Ottokar Tumlirz described careful and effective experiments which demonstrated the effect of the rotation of the Earth on the outflow of water through a central aperture. The subject was later popularized in a famous article in the journal Nature, which described an experiment in which all other forces to the system were removed by filling a 6 ft tank with 300 U.S. gal of water and allowing it to settle for 24 hours (to allow any movement due to filling the tank to die away), in a room where the temperature had stabilized. The drain plug was then very slowly removed, and tiny pieces of floating wood were used to observe rotation. During the first 12 to 15 minutes, no rotation was observed. Then, a vortex appeared and consistently began to rotate in a counter-clockwise direction (the experiment was performed in Boston, Massachusetts, in the Northern Hemisphere). This was repeated and the results averaged to make sure the effect was real. The report noted that the vortex rotated, "about 30,000 times faster than the effective rotation of the earth in 42° North (the experiment's location)". This shows that the small initial rotation due to the earth is amplified by gravitational draining and conservation of angular momentum to become a rapid vortex and may be observed under carefully controlled laboratory conditions.>>[/quote][/quote]
That article is misleading, neufer. Obviously, there are ways to counteract the "natural" direction of the water spiral, or to stop it spiralling completely. Many sinks are too small to observe any spiral (without forcing one). And toilets in Australia typically have a lower water level than toilets of American design, so Australian toilets are much more turbulent and typically never spiral when flushed. But bathtubs are typically big enough to produce a spiral when draining, and statistically speaking, water draining from bathtubs in the Southern Hemisphere will have a slight tendency to spiral in the opposite direction, compared with the Northern Hemisphere. And again, statistically, bathtubs that are closer to the equator tend to take slightly longer to drain.