Is there Coriolis force at the equator?

[Eagle1]

A question to all the Met. wizz-kids (or anyone else, for that matter).

I just studied the subject of Coriolis force, and noticed that the force has to do with the latitude and angular velocity. Now, I always thought that at the equator angular velocity would be higher than at the poles, so, I, innocent student, thought that there would be more Coriolis force at the equator - and, suddenly, the book tells me that that's not the case, and that there's no Coriolis force at all at the equator. I would think that there would be less force at the poles, simply because there the surface of the earth hardly has any rotating speed.
I saw the formula, which says that Coriolis force has to do with the sinus of the latitude, but it just doesn't convince me (I'm more a person for plain language, I'm afraid).

Anyone who can shed some light? It would be much appreciated.

[1515Blue]

that is one subject i've never completely understood... especially how it affects wind patterns etc

[francine]

I am by no means a whiz, so somebody please correct me if I'm completely off the mark, but the way I understand it is like this: rotatation at the poles is 'tighter' (smaller rotations = more force generated), and 'lazier' at the equator, hense less force. Sorta like the inside and outside of a turn.

I'd love to hear from a higher authority on this one!

cheers!

[Fresca]

As I have understood it, it is due to the rotation of the Earth.

If one is stationary at the equator, hten one is moving at some speed which is the rotational speed of the Earth. If then one moves directly to the North, then the rotational speed of the Earth is the decreses but the angular speed is the same, due to smaller radius of the circle. Therefore one is moving at the same rotational speed as eqator, which is higher than at this northern lattitude, and it comes out as a turning force. The same happens when going from north to the Equator, one's speed is less then the Earths at the lower lattitudes, which comes out as a turning force.

Please correct me if this is far off:eek:

['%MAC']

Mother Earth rotates counter-clockwise when viewed from the North Pole at a given speed of 15.04* / hr. At the equator this speed corresponds to 903 nm / hr. If we travel from the Equator to 30* north or south latitude, the Earth rotates at the same rpm, but the relative speed is 781 nm / hr. Now if we are a parcel of air and we proceed to go in either one of these directions, from the equator, we are traveling at a greater speed then the earth below so we move to the right when viewed from the ground. If we are at 30* north and at our relative velocity of 781, then moving to the south will mean that we are slower then the equatorial speed of 903, and we will fall off to the left. Same thing if we are south and move north to the Equator, we will fall off to the left. The Coriolis force is a perceived force that we use while we are spinning about, the fault can be traced back to Newton and his insistence that an object continue in a straight line, unless acted upon by an outside force. Now to the particle of air it is moving in a straight line, but to the casual observer on the ground, the particle seems to curve right if it's increasing latitude, or left if it's decreasing latitude. It's about changing your frame of reference. Be the particle.....and you travel straight, be the observer and you see a curve.

The magnitude of the Coriolis force can be reduced to the form:
2vwsin (latitude)
Where
V = velocity of object in question
w = angular velocity of Earth, 15.04 deg / hr or 7.292116X10-5 rad/sec

So you can see at the Equator the sin of 0 is 0, there is no relative deflection, and at the pole the sin of 90 is 1 so you have your initial velocity coupled with your angular velocity. So a particle of air at the poles is blowing at 903 nm/ hr, and that is why it is such a harsh environment and most people want to live at the lower latitudes. Besides, as speed increases time slows down, so you live longer at the Equator.

[Checkboard]

Imagine a record turntable. (Remember those things before CDs? :) ) Now looking at the turntable from above, an abject placed in the centre will have a speed of zero - it is just spinning around, not going anywhere.

An object placed on the edge will have the greatest speed, as it zooms around the outside of the circle.

Now stop the record player, and chalk a straight line from the centre to the edge. With the record player stopped, there would be no problem walking along this straight line (if you where small enough.)

Now start the record player up again. shrink yourself and stand in the centre - your speed is zero (you are just spinning around) and in front of you is the straight chalked line. After things have settled down, and the fluid on your inner ear has matched the speed of rotation of the record player, you do not notice that it is spinning - it looks stationary to you.

Now for the sobriety test - you start walking along the straight line you have chalked. With each step towards the edge of the record player you actually have to "speed up" to match the speed of the bigger circle you have stepped into. When the record player was still, walking the line was no problem. but now that it is turning, with each step you feel forced to the left (for a clockwise spinning player). This "force" you feel is the reaction to the acceleration necessary for you to speed up to match the speed of the greater circle you have stepped into, and is termed the "coriolis force".

It is an imaginary force we use to explain an apparant "force" in an accelerating (turning) frame of reference, when we consider that frame to be stationary.

Why does it get less towards the equator? On our record above, as you approach the edge, it wouldn't get less.

Look at the Earth from the North pole, looking down. You see a "circle" turning anti-clockwise. because you are looking at a globe, one step from the North pole towards the equator is the same as one step on the circle, but the Earth's surface is curving away from you - so each step on the Earth's surface is a smaller step towards the "edge of the circle" until you reach the equator where each step is simply a step away from the north pole, and doesn't move you towards the edge of the circle at all.

[bookworm]

Here's a physics-based way of looking at it.

The Coriolis force depends on the vector (cross) product of the angular velocity of the rotating frame and the velocity of the object. That means that it acts perpendicular to both of those vectors, and depends on the sine of the angle between them.

At the equator, there are two cases to consider. Moving north-south, the velocity is in the same direction as the angular velocity of the rotating frame (parallel to the earth's rotation axis). So the cross product is zero -- no Coriolis force.

Moving east-west, the velocity perpendicular to the angular velocity of the rotating frame, so you feel the full effect of Coriolis force. However, the force is perpendicular to the velocity and the axis of the earth -- in other words it acts in the local vertical, away from the centre of the earth. So it's not apparent in the usual way.

Strictly speaking, Eagle1's book should have said that at the equator there is no component of the Coriolis force in the horizontal plane.

[The man formerly known as]

Checkboard

This is all related to the way water goes down plug holes. Does it go down differently in the north and south hemisphere and on the equator does it just glug?

I notice you are from the south so which way does it go down in Australia Clockwise or Anticlockwise. I meant to look the last time I was down there but forgot.

Also I stopped over in Singapore which if I recall rightly is pretty near on the equator but I do recall the water swirling down the hole in one direction or the other and not just glugging down the middle as I expected. Do you need to be smack on the equator for the water to glug? Perhaps a pruner on the equator can shed some light?

['%MAC']

Sorry to say that on such a small scale the Coriolis force has not much influence. The rotational direction water travels is due to the design of the facility or prior movement of water. In a laboratory setting it may be possible to get the water stable enough to be influenced by the Coriolis force, but in a house just walking up to the sink will produce vibrations that will influence the water. Even larger scale phenomena are not readily affected by the Coriolis force, tornados and rotational microbursts can go either way. It’s only really big stuff, like hurricanes and typhoons.

[Eagle1]

Thanks for all the answers, guys. I'll take some time to read these answers carefully, and if things are still a bit unclear I'll come back to you.
Not surprising I'm not the only one who has difficulty understanding this matter, but nice to see all the truly international reactions!

Greetz, Eagle1

[Brenoch]

I recon the bog just won´t flush at the equator.. :D :D :D