# Coriolis effect and water spin

#### Jack

If the coriolis effect does not determine the direction in which water drains down a plug hole in different parts of the world then is it totaly random which way the water spins.

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No, it's not totally random. The coriolis force is one of the forces acting on the water, but it's proprtional to speed and the sine of the latitude, so in most drain situations it's pretty small, and is swamped by the local forces arising from the shape of the basin, the previous motions of the water (conservation of angular momentum) and so on. It's all determinate and may possibly be chaotic, but it's not random.

#### Jack

What I meant was does water always drain a certain way in different parts of the world?

#### emu

Yes, water always drains the same way in the same hemisphere. I believe the effect is weakest at the equator but I'm not sure about that one.

#### Jack

Originally posted by emu
Yes, water always drains the same way in the same hemisphere. I believe the effect is weakest at the equator but I'm not sure about that one.
Therefore my point is why? If the coriolis effect only effects large fluids such as hurricanes then why does water always drain the same way in the same hemisphere?

#### STAii

In smaller fluids, put the coriolis affect aside.
Now there are a big number of factors that will affect how the water drains (see selfAdjoint's post), if all those factors were re-made the same way in the experiment of water drain, then the water will drain exactly the same way.

I don't see how you are trying to connect the coriolis effect to this, the coriolis effect will be neglible and you can almost forget about it in similiar situations.

#### MrCaN

The coriolis effect doesn't determine the way a drain drains. And they don't drain the same way everywere on the hemisphere. Now most drains do drain the same way, because they are made the same way, that is they are all spun the same way when polished, producing grooves that determine the flow down the drain.

#### Jack

Originally posted by MrCaN
The coriolis effect doesn't determine the way a drain drains. And they don't drain the same way everywere on the hemisphere. Now most drains do drain the same way, because they are made the same way, that is they are all spun the same way when polished, producing grooves that determine the flow down the drain.
So do you mean it has nothng to do directly with position of the earths surface?

#### chroot

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Originally posted by Jack
So do you mean it has nothng to do directly with position of the earths surface?
Not a thing.

- Warren

#### Jack

Surely that can't be true! So you could bring an Australian sink over to England and the water would drain the same way?

#### rdt2

Originally posted by Jack
Surely that can't be true! So you could bring an Australian sink over to England and the water would drain the same way?
It might, it might not. The point is that, on this scale, the Coriolis force is swamped out by other influences.

Cheers,

Ron.

#### Jack

I realise that now it's just i'm still confused firstly as to weather there realy is a difference between the direction in which water spins in the two hemispheres and secondly, if it does, why does it if it's not due to the coriolis effect?

#### chroot

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Originally posted by Jack
I realise that now it's just i'm still confused firstly as to weather there realy is a difference between the direction in which water spins in the two hemispheres and secondly, if it does, why does it if it's not due to the coriolis effect?
Didn't this thread answer both of those questions in detail already?

- Warren

#### RuroumiKenshin

Does the corioulis force affect the way we think? electricity? the weather?

#### damgo

No, no, yes. Large-scale weather patterns are affected by the Coriolis effect: it causes cyclones to rotate in oppoosite directions in the two hemispheres; the trade winds around the Equator to bith point west; and the jet streams in both hemispheres to point east.

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Originally posted by MrCaN
The coriolis effect doesn't determine the way a drain drains. And they don't drain the same way everywere on the hemisphere. Now most drains do drain the same way, because they are made the same way, that is they are all spun the same way when polished, producing grooves that determine the flow down the drain.
It is possible to make drains in lab conditions where all the other forces are minimised, and then the water drains according to what the coriolis effect says.

The coriolis effect is a force that acts on every moving thing. It is proportional to the speed and to the trigonometric sine of the latitude. It acts to the right if the velocity vector of the moving thing in the Northern hemisphere and to the left in the Southern hemisphere. But the effect is very weak, and it really shows up only when a lot of little things are all going the same way, as in air or ocean movements.

The effect of the sine dependence: There is no coriolis at the equator. It is half its maximum strength at 30o latitude, 71% at 45o, 87% at 60o, and 100% at the poles.

#### damgo

For the record, the Coriolis force is given by

F = -2m(w x v)

where w=7.292e-5 /sec is the angular velocity of the Earth. So at the Equator, the Coriolis force vanishes for horizontal motion, but gives maximum deflection for vertical motion.

Roughly, this corresponds to a deflection of about 10 degrees/hour from a straight trajectory for a freely moving object around the middle of one of the hemispheres.

#### Bobby R

Coriolis(Carioles) effect

Carioles Effect: Since the Carioles Effect causes moving particles to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere and the deflection is proportional to the speed and latitude of the moving particles; water should flow straight down on the Equator, clockwise north of the equator and counter-clockwise south of the equator. Additionally, the further north or south one goes the faster the spin. However, using the common drain for your experiment allows for other forces which may not yield the results you are looking for. Bear in mind also that the speed of effected particles already in motion will be unchanged by the apparent deflection.

#### NEOclassic

Re: Coriolis force (Google)

Hi Bobby and Jack and all you Middle and High school students in this string,
To understand the Coriolis Force you must first understand the math of the "cross-product" of vectors. Its the only true "product" of vectors (the diagonal of a parallelogram is actually a vector sum or resultant)and is comprised thusly: with two vectors arranged tail to tail at the x-y origin there will be a cross-product vector along the z-axis whose scaler value is the product of the original scalars. IOW, resultant is always perpendicular to the plane of the original vectors.
For example, a circular loop of electron current will be manifest as a magnetic dipolar field that is pointed in the direction perpendicular (normal)to the plane of the loop. This is called the "right-hand-rule." Analogously, when matter possesses angular momentum there is a vector called "torque" that is perpendicular to plane of angular momentum; the rotating mass of the earth maintains a strong torque axis directed toward Polaris.
In the physics lab at your school there are several experimental devices that furnish the hands-on feel of the Coriolis force; the one with the most dramatic "feel" is the bicycle wheel with handles affixed to the hub - you hold the wheel by the handles and a colleague spins the wheel - you try to turn to your right and you feel a tug bending the wheel toward the floor. If the teacher has a "topsy top" that turns upside down he may share it with the class - it behaves as a response to the Coriolis force.
In a coin, drill a small hole near the edge of the coin; spin the coin and observe that, although you might expect that the lighter mass would cause the hole to rise to the top of the spin axis, the contrary is true - If you would like to see the "hole" rise, stuff a lead slug in the hole.
The upshot of the Coriolis force is that the affected matter must have angular momentum. Before the water going down the spout of the bathtub starts to spiral. its original twist is more likely to have been caused by Bernoulian phenomena. My personal belief is that all the weather cyclic behavior is somehow a consequence of the earth's tangential velosity (of < or = about 1000 mph) coupled with the viscosity of the atmosphere. Cheers, Jim

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