Posts Tagged ‘clockwise’

earth's rotation, coriolis effect, clockwise, anti-clockwise, atmosphere, ocean, hemisphere

Due to the earth’s rotation, the Coriolis force deflects the atmosphere, oceans, and large objects on the surface of the Earth in an anti-clockwise direction in the northern hemisphere, and clockwise in the southern hemisphere

You may have heard that water flowing down the plug hole in a sink or bath always swirls anti-clockwise in the Northern Hemisphere, and clockwise in the Southern Hemisphere, and that this is due to the Coriolis effect.

The Coriolis effect (or Coriolis force) was first postulated by the French scientist Gaspard-Gustave Coriolis in relation to the behaviour of water wheels in 1835, but so far as the Earth is concerned, it is the deflection of the atmosphere and the oceans, and large objects on the surface of the Earth, due to the earth’s rotation around its axis. Cyclones, and jet streams in the upper atmosphere, are two of the more obvious phenomena caused by the Coriolis effect, but the effect also causes certain types of waves to form in the oceans. However because the earth spins relatively slowly, the apparent force that its rotation generates only becomes significant over large distances or long periods of time.

paris gun, first world war, bombardment, coriolis effect, trajectory

In the First World War, the Paris Gun was used to bombard Paris from a range of about 120 km (75 miles). Because of the distance, the Coriolis effect had to be taken account of in the calculations of the trajectory.

The Coriolis effect became important in external ballistics for calculating the trajectories of very long-range artillery shells. The most famous historical example was the Paris gun, used by the Germans during the First World War to bombard Paris in 1918 from a range of about 120 km (75 miles). The distance was so far that the Coriolis effect was substantial enough to affect trajectory calculations. Incidentally, the shells of the gun reached a height of 40 kilometers (25 miles, 131,000 ft) and were the first man-made objects to reach the stratosphere.

However, the direction in which water flows down a plug hole is not influenced by the Coriolis effect, which is tens of thousands of times weaker than other factors such as the existing disturbance in the water, the angular momentum that causes the initial vortex, and the shape of the bowl.

bart simpson, anti-clockwise, coriolis effect

Bart Simpson notices that the water flows down the toilet in an anti-clockwise direction

Despite this, popular entertainment has maintained interest in the Coriolis effect. Bart vs. Australia, the sixteenth episode of the sixth season of The Simpsons, starts with Bart Simpson noticing that the water in his bathroom sink always drains anti-clockwise (counterclockwise in the USA). Bart does not believe Lisa, his sister, who explains that this is due to Coriolis effect, and that in the southern hemisphere the water drains the other way round. To confirm this, Bart makes phone calls to various countries in the southern hemisphere, ending up with a call to Australia. Here a little boy, who lives in the outback, confirms, having also checked with his neighbours, that the toilets and sinks are all draining clockwise. The plot continues with Bart being sued by the boy’s father for the cost of his six-hour ‘collect’ call, with Australia indicting Bart for fraud, the USA wanting to send him to prison to placate the Australian government, Bart having to make a public apology in Australia, and so on.

However in 1962, Ascher Shapiro, a researcher at the Massachusetts Institute of Technology in Boston, USA, was able to demonstrate the Coriolis effect on draining water, and this was later repeated by scientists in Sydney, Australia.  But this was only achieved by using a perfectly circular bath 1.8m in diameter  and 15cm deep, and by allowing the water to stand for 24 hours so that any currents from filling would die down. A small outlet, on the outside, meant that the water took about half an hour to drain away. Under these conditions, the Boston researcher reported a tendency for water to swirl anti-clockwise (viewed from above), whilst the scientists in Sydney described seeing water swirling clockwise.

So to observe the Coriolis effect at home, you would need a large but shallow circular bath, and one that’s not affected by any vibration or disturbance, as well as plenty of time.

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diana princess of wales, fountain, hyde park, london, anti-clockwise

Diana, Princess of Wales Memorial Fountain, Hyde Park, London.
Children are walking along the fountain in an anti-clockwise direction

I was at the Diana, Princess of Wales Memorial Fountain in Hyde Park, London, a few weeks ago with my eight-year old grand-daughter. As the official website says ‘water flows from the highest point in two directions as it cascades, swirls and bubbles before meeting in a calm pool at the bottom’. Although the information on the site says visitors should ‘feel free to sit on the edge of the Memorial and refresh your feet’, it adds ‘visitors are asked not to walk on the Memorial’. Well when I was there, on a pleasant sunny weekday afternoon, it is hardly surprising that a couple of hundred children were walking and running all over the circular memorial having some outdoor fun.

My grand-daughter completed about a half a dozen circuits of the fountain, following and then passing groups of children, never seeming to get tired of going round and round. Then all of a sudden she was walking through the water in the opposite direction to virtually everybody else. Well, so what? But it struck me that everyone was moving in an anti-clockwise direction around the fountain (counter-clockwise in the USA). There wasn’t a notice telling the children that they had to move in a particular direction (after all they were only supposed to be splashing their toes in the water), nor was there any discernible difference between the two halves of the circular fountain that might influence the direction that the first children to arrive at the fountain in the morning, might take. Obviously once the early arrivals went in one direction, then the others coming after would be influenced to walk in the same direction, but was anti-clockwise the preferred direction?

roger bannister, athlete, running, oxford, four-minute mile

Roger Bannister becomes the first person to break the four-minute mile, running anti-clockwise, at the Iffley Road track in Oxford on 6 May 1954, in a time of 3 min 59.4 sec

Athletes on tracks throughout the world run in an anti-clockwise direction. ‘Left hand inside’ was adopted at the first London Olympics in 1908 and it has been used ever since. However the UK Amateur Athletic Association left open the choice of direction and as late as 1948, Oxford University athletes still ran clockwise. Some of the reasons advanced for this are, firstly, that with the majority of humans being right-handed, the same applies to your feet, so you push off with your right foot, and you are automatically steered in an anti-clockwise direction. Secondly, with the heart being on the left-hand side of our bodies, running anti-clockwise is more comfortable and reduces the stress on the heart.

One study though showed that statistically people tend to turn left more easily than right, although the variability is large. This may suggest that running in a left-hand turn (anti-clockwise) is easier than in a right-hand turn (clockwise). But why? Well the study concluded that ‘veering is related to a sense of straight ahead that could be shaped by vestibular inputs’. Whatever that means, it suggests that the two reasons given earlier are incorrect.

The anti-clockwise rule also applies to ice-skating, roller-skating, ballroom dancing, and apparently to aircraft in the circuit waiting to land. But this doesn’t seem to prove much as it doesn’t apply to horse-racing, which can be clockwise or anti-clockwise, nor to motor racing, which is predominantly run clockwise.

But for the children going round the Memorial Fountain, it does seem that anti-clockwise is their preferred direction.

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