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Coriolis Effect


Let us suppose that a pilot has drawn a straight line from Delhi to Mumbai and has started travelling the same path, his plane will never reach to Mumbai, and rather his plane will go inside the Arabic sea. He wants to reach Mumbai; he has to shift his plane to its left continuously. Moving things which are in the atmosphere of earth, like sea water, rivers, air, birds, missiles etc, they deflect from their original path. Things which are in north hemisphere of earth, deflects toward right. Things which are in south hemisphere of earth, deflects toward left. This happens only because of rotation of earth around itself. This is known as ‘Coriolis Effect’. Actually Coriolis was one of the great mathematicians. He was the person, who for the very first time explained the reason behind the deflection of moving objects.

On the north & South Pole of earth, where the velocity of earth rotation is maximum, this effect can be seen more prominently at those locations. Towards the equator, this effect starts decreasing and at equator, it becomes zero. The Coriolis Effect also depends upon the speed of moving object.

During the First World War, German soldiers utilised very big missile named   ‘BIG BERTHA’ to dismantle Paris city. For a distance of 70 miles, this missile bomb takes 3 minutes. Due to Coriolis Effect, bomb had deflected from its original path. Its deflection was nearly of 1 mile from its target. Thus, Coriolis Effect saved Paris city from damage.

One more interesting example of Coriolis Effect is described below. Let us suppose that from North Pole we have set one missile targeting New York City. Now consider that bomb fired from missile requires one second to cross the distance of one mile and it is moving steadily. Accordingly, by this speed, it will require fifty five seconds. During this time period New York City is moving with speed of eighteen mile per second in space, as earth is revolving with this same speed around sun. By the way, line of altitude is moving with speed of 15 degrees per hour. Because of this two types of motions, at the end of 55 seconds bomb will not damage to New York, rather it will fall on city Chicago which is in north-west.

Because of the earth’s rotation, any freely moving  object or fluid will appear to:

Turn to the right of its direction of motion in the Northern Hemisphere and

Turn to the left of its direction of motion in the Southern Hemisphere.

(For example, note the curved wind arrows in the diagram below.)

This causes winds to travel clockwise around high pressure systems in the Northern Hemisphere, and counter-clockwise in the Southern Hemisphere.

Low pressure winds travel in the opposite direction (counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere).

Because of the Coriolis Effect, winds travelling along the surface of the earth from 30 – 60 degrees north and south of the equator flow from the west to the east.  These winds are referred to as the westerlies.


Idealized global circulation

The air currents moving along the surface of the Earth from the poles (90 degrees) to 60 degrees north and south of the equator, flow from east to west and are referred to as the polar easterlies.

On earth, there is a lot of loss take place because of cyclones. Loss which is taking place because of cyclones is really very severe. The formation of cyclones is result of Coriolis Effect. On this statement nobody can rely.

Now let’s see what exactly happen thereby. Suddenly in the atmosphere of earth, if there is formation of belt of less pressure, air from high pressure zone immediately tries to rush to less pressure zone. This is the property of flow of air. Now let’s suppose that this kind of belt of less pressure is formed in Northern Hemisphere of Earth. Coriolis Effect will not allow this air to flow in straight path. Path of air flowing from any direction of earth will be deflected to right side. For example, blow of air coming from East will be deflected to South, blow of air coming from West will be deflected to North, blow of air coming from North will be deflected to East, and blow of air coming from South will be deflected to West. The combined effect of all these, is that around the area of less pressure formation of very dangerous cyclones takes place.

In this way zone of formation of cyclones is very big. If such kind of cyclone formation takes place on the surface of sea water, it is used to carry away very big ships also. Only because of rotation of earth about itself carries this kind of adverse effects.

But, the Coriolis force is very small indeed.

Compared to the rotations that one usually sees (tires on a travelling automobile, a compact disc playing music, or a draining sink), the rotation of the Earth is very small: only one rotation per day. The water in a sink might make a rotation in a few seconds and so have a rotation rate ten thousand times higher than that of the Earth. It should not be surprising, therefore, to learn that the Coriolis force is orders of magnitude smaller than any of the forces involved in these everyday spinning things. The Coriolis force is so small, that it plays no role in determining the direction of rotation of a draining sink anymore than it does the direction of a spinning CD.

In this way, there are both advantages & disadvantages of Coriolis Effect. You can also experience this effect & will come to know effect of it on our daily life.

-Nikita G. Nenwani (Btech Mechanical).

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