Response from First Day of Class

            My name is Liza Zipursky, I’m 24 years old, and I am currently a student at BU’s Metropolitan College, majoring in Psychology. This summer, in addition to taking classes, I am a research assistant at the Center For Anxiety and Related Disorders at BU. I was born and raised in Los Angeles, California but have been living in Boston for five years, and currently live in Jamaica Plain. I have had the great fortune on traveling around the world, and have also lived in Vermont, New York City, Paris, and Thailand. I love to socialize and also DJ on the side. I can’t wait to see what we will find in our exploration of the Boston Harbor!

            In our group observation today we looked at the direction in which the water rotated when draining in a sink in the women’s bathroom. We watched as the water drained and did not see in rotating in a particular direction until the very end where the water created a vortex and spun clockwise. All members in our group were in agreement that we observed the water draining in a clockwise direction.

            When I was about 11 years old I made a trip to Australia and remember my Dad telling me that the water spun counter clockwise because we were in a different hemisphere. So I assumed that the way water spins depended on the Hemisphere until I did some online research and found that what my dad had told me was actually a myth.

            First, I watched a youtube video, http://www.youtube.com/watch?v=WBsYaudxjWg, that showed a man testing this theory. It showed water draining counter clockwise in Australia, a country in the Southern Hemisphere, but much to my surprise he tested the direction in which the water drained in Hong Kong, a city in the Northern Hemisphere and water drained counter clockwise there too!

            I then found this, “A popular misconception is that the Coriolis effect determines the direction in which bathtubs or toilets drain, and whether water always drains in one direction in the Northern Hemisphere, and in the other direction in the Southern Hemisphere. This myth is perpetuated by the Simpsons episode "Bart Vs. Australia." In reality, the Coriolis effect is a few orders of magnitude smaller than other random influences on drain direction, such as the geometry of the sink, toilet, or tub; whether it is flat or tilted; and the direction in which water was initially added to it. Note that toilets typically are designed to only flush in one rotation, by having the flush water enter at an angle. This is less of a puzzle once one remembers that the Earth rotates once per day but that a bathtub takes only minutes to drain. When the water is being drawn towards the drain, the radius with which it is spinning around it decreases, so its rate of rotation increases from the low background level to a noticeable spin in order to conserve its angular momentum (the same effect as ice skaters bringing their arms in to cause them to spin faster).” From the website http://www.funtrivia.com/askft/Question75645.html. Under this post there was a like to Wikipedia on the Coriolis Effect.

            I clicked in the link to Wikipedia and found the following under the section, “Draining in Bathtubs and Toilets”, In 1908, the Austrian physicist Otto 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.[27] 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-foot (1.8 m) tank with 300 US gallons (1,100 l) 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.

In contrast to the above, 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 pulls 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 (once per day at the poles, once every 2 days at 30 degrees of latitude) 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,[30] such as any residual rotation of the water[31] and the geometry of the container.[32] Despite this, the idea that toilets and bathtubs drain differently in the Northern and Southern Hemispheres has been popularized by several television programs, including The Simpsons episode "Bart vs. Australia" and The X-Files episode "Die Hand Die Verletzt".[33] Several science broadcasts and publications, including at least one college-level physics textbook, have also stated this.” This quote comes from http://en.wikipedia.org/wiki/Coriolis_effect#Draining_in_bathtubs_and_toilets. 

-Liza Zipursky