[extropy-chat] FWD [forteana] The great plughole debate [Coriolis effect]

[Terry W. Colvin]

< http://www.guardian.co.uk/life/feature/story/0,13026,1083412,00.html >

The great plughole debate 

Does water really swirl in the opposite direction south of the equator? Well, 
yes and no, finds David Adam 

Thursday November 13, 2003
The Guardian 

In the gents toilets at Quito airport in Ecuador last month I had one of the 
most disappointing experiences of my life. The flight from London had been a 
long one, and feeling queasy over the last few hours all I wanted to do was get 
off the plane, head for the lavatory and hold my head over the sink. Yet when I 
finally got my wish, as the water gurgled down the plughole just a few inches 
from my face, I felt nothing but disillusionment and a desperate sense of 
anticlimax. 

The reason for my disappointment was this: most people have heard that the water 
swirls the opposite way down the plughole in the southern hemisphere. This is 
supposedly due to the Coriolis force, an invisible hand primed by the rotation 
of the Earth to nudge fluids into rotating anticlockwise north of the equator 
and clockwise to its south. The idea permeates popular and scientific culture; 
it has cropped up in the Guardian's Notes and Queries section, is regularly 
referred to during school lessons and appears in the occasional physics 
textbook. Some Australians even see their backwards working dunnies as one of 
their proudest national symbols. 

What is less well established is that, if this effect switches the flow 
direction as you pass from north to south, then at the exact point of the 
equator these opposing forces should balance perfectly and the water in a 
draining sink should pour straight down. 

Yet at Quito airport, this was plainly not the case. Even in Ecuador, a place 
with such an affinity to the equator they named the country after it, the water 
continued to spin itself into a miniature whirlpool. Cold tap, hot tap, gushing 
torrent or little more than a drip, it made no difference. Each time, the water 
stubbornly spiralled its way down the plughole. A couple of times it hesitated, 
as if undecided which way to turn, but turn it always did. 

Across the country it was the same story. From the dense Amazon jungle in the 
east to the lush reserves that hug the Pacific coastline, each time we arrived 
in a new place I would enter the nearest public convenience with renewed hope, 
only to emerge crestfallen. Most frustrating of all was the failure of the water 
to behave as expected within spitting distance of a mighty concrete monument 
erected to sit exactly on the equator itself. (This was doubly frustrating as 
someone had stolen the plug and it took me several minutes to work out how to 
use the palm of my hand instead.) 

Noting my dejection, a waiting bus driver asked me what was wrong and using 
broken Spanish I explained. His eyes lit up, and in conspiratorial tones he told 
me an incredible story. He said (I think) that the giant concrete monument was 
actually in the wrong place, that modern GPS measurements had revealed the true 
location of the equator to be further north, and in this place the water really 
did pass straight down the plughole. And, most importantly, he said he would 
take me there. 

This seemed too good an opportunity to miss, and even when we were paying our $3 
to enter what looked suspiciously like his mate's back garden, through which the 
true equator apparently ran, the alarm bells remained silent. In the garden was 
a sink. The sink was about 4ft high, full of water and was standing over a 
painted yellow line on the ground. Unlike the bus driver, the sink owner spoke 
excellent English, and, holding a model globe, he explained about the Coriolis 
force. The Earth spins to the east, he said, completing one full revolution a 
day. To get round in a day, a point on the equator spins at about 1,000mph, 
while one 100 miles from the north pole only moves at about 20mph, because the 
distance it must travel is much shorter. This difference in speed means that 
fluids travelling across the globe are effectively deflected, causing them to 
spin. 

And then he removed the plug. And I watched the water go straight down. 

He refilled and drained the sink twice more - once a few metres north of the 
line, where the water instantly gained an anti-clockwise twist, and then to the 
south, where it went round clockwise. It was an impressive show, and back in 
Britain I dined out on the story for several weeks (and nobody including several 
scientists, may I point out, ever questioned it). But then, disaster struck. 

Bored one wet lunchtime, I idly investigated the phenomenon, only to read about 
the same demonstration being carried out in Kenya to "gullible tourists" by 
"charlatans". My pride stung, I made some calls. My pride stung still further 
when the hoax was confirmed. 

Despite what you may hear or read, even in some scientific text books, it turns 
out that the Coriolis force has absolutely no effect on the direction that the 
water drains from an everyday sink, toilet, shower or bath. It does affect the 
spin of ocean currents and weather systems such as hurricanes, but on the small 
scale of a domestic sink the Coriolis force is tiny, and is simply dwarfed by 
other factors such as the sink shape, differences in temperature or, most 
likely, residual currents lingering from when the sink was filled with water. 

That's not to say it's impossible to see the effect of the Coriolis force in a 
sink, as two little-known papers in the science journal Nature demonstrate. The 
secret is to eliminate all the interference, and in 1962 in the appropriately 
named Watertown, Massachusetts, the physicist Ascher Shapiro did just that. 
Built in a windowless room, Shapiro's circular sink was about two metres across 
and 150mm deep, with a tiny hole drilled in the middle that could be unplugged 
from below. After filling the sink with water, he left it to stand for more than 
three days. It took nearly an hour-and-a-half to drain, and sure enough the 
water went anticlockwise each time. Three years later, a group at the University 
of Sydney repeated the experiment, and as long as the water was allowed to stand 
for at least 18 hours, it always went down the plughole in a clockwise 
direction. "We have acquired confidence in the hypothesis that carefully 
performed experiments on liquid drainage from a tank will show clockwise 
rotation, if done in the southern hemisphere," they concluded. 

And me? I decided to put my experience to use. After a few days splashing around 
in my bathroom sink, I can make the water go down the plughole any way I choose. 
And for a small fee, I'm happy to demonstrate how the equator runs through north 
London.


-- 
“Only a zit on the wart on the heinie of progress.” Copyright 1992, Frank Rice


Terry W. Colvin, Sierra Vista, Arizona (USA) < fortean1 at mindspring.com >
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