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Coriolis effect - angular momentum not conserved?


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The Coriolis effect causes water to spiral down and out of

a draining sink.

Maybe someone could tell me how angular momentum is

conserved when circular sink full of water is drained

and the draining water leaves the sink with unaccountable

angular velocity?

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The Coriolis effect causes water to spiral down and out of a draining sink.

That's an urban myth. It's not true. The Coriolis effect is far to weak to have any noticeable effect on how water drains from a kitchen sink.

Maybe someone could tell me how angular momentum is conserved when circular sink full of water is drained and the draining water leaves the sink with unaccountable angular velocity?

If you fill the sink and then immediately pull the plug, there most likely is some residual angular momentum from the act of filling the sink. This is the key reason you see the water start spinning in a sink or a tub as it drains. Any asymmetries such as an off-center drain hole (e.g., a typical bathtub) will add to this effect.

 

Suppose you do the experiment right:

  • Get your hands on a very large, perfectly circular sink with a small drain in the very center.
  • Close the drain and fill the sink with water.
  • Let the water stand for several days so as to damp out any angular momentum that was added when you filled it.
  • Open the drain.
After hours have passed (this is why the drain has to be small) you will start seeing a circulation in the water that remains in the sink. This rotation does come from the Coriolis effect.

 

So why isn't angular momentum conserved?

 

Simple. First off, you're looking at things from the perspective of a non-inertial frame. Secondly, you're not looking at a isolated system. Conserved quantities (linear momentum, angular momentum, and energy) aren't necessarily conserved in non-inertial frames, or in non-isolated systems.

Edited by D H
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That's an urban myth. It's not true. The Coriolis effect is far to weak to have any noticeable effect on how water drains from a kitchen sink.If you fill the sink and then immediately pull the plug, there most likely is some residual angular momentum from the act of filling the sink. This is the key reason you see the water start spinning in a sink or a tub as it drains. Any asymmetries such as an off-center drain hole (e.g., a typical bathtub) will add to this effect.

 

Suppose you do the experiment right:

  • Get your hands on a very large, perfectly circular sink with a small drain in the very center.
  • Close the drain and fill the sink with water.
  • Let the water stand for several days so as to damp out any angular momentum that was added when you filled it.
  • Open the drain.
After hours have passed (this is why the drain has to be small) you will start seeing a circulation in the water that remains in the sink. This rotation does come from the Coriolis effect.

 

So why isn't angular momentum conserved?

 

Simple. First off, you're looking at things from the perspective of a non-inertial frame. Secondly, you're not looking at a isolated system. Conserved quantities (linear momentum, angular momentum, and energy) aren't necessarily conserved in non-inertial frames, or in non-isolated systems.

 

I agree with you but the problem is the net angular momentum of the water from the Coriolis effect in the sink is less than

than the net angular momentum of the water leaving a small circular drain in the center of the sink which can easily

be confirmed from a simple visual inspection. I think this should be more thoroughly investigated by the scientific

community to find out whats going on.

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If you do this experiment at the geographic north pole

the angular momentum of the water in the sink before

it was emptied is negligible. The angular momentum

of the water exiting the sink is easily observable not

to be negligible.

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I'm fairly sure that the poles are the only two places that you won't get a Coriolis effect.

 

Do you not understand that it's nothing "unexpected"?

If you put your hand in the water and stir it, the water spins.

Do you think that is a breach of the conservation of momentum?

 

Did you not understand this comment

" Secondly, you're not looking at a isolated system. Conserved quantities (linear momentum, angular momentum, and energy) aren't necessarily conserved in non-inertial frames, or in non-isolated systems."

from DH?

Edited by John Cuthber
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I think this should be more thoroughly investigated by the scientific

community to find out whats going on.

The scientific community is pretty satisfied they know what's happening. Though it appears that you do not. Feel free to ask questions until this misconception is cleared up. But, you may want to dial back the attitude that just because you don't understand something, that automatically means everyone doesn't understand it.
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I agree with you but the problem is the net angular momentum of the water from the Coriolis effect in the sink is less than

than the net angular momentum of the water leaving a small circular drain in the center of the sink which can easily

be confirmed from a simple visual inspection. I think this should be more thoroughly investigated by the scientific

community to find out whats going on.

This is a Figure about the coriolis effect.

The first Figure is about the height effect, and then, the second Figure is about the latitude effect.

coriolis.jpg

coriolis2.jpg

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It seems according to what I did that it may actually be a myth. I tried pouring water down my sink 3 different ways. From the left side, the right side and the middle. When I poured from the left side, the water went clockwise. When I poured water from the right, the water drained counter clockwise. When I poured down the middle, the water became split around the drain and entered going in both directions from either side. I did not notice any change in velocity in the water flows when compared to each other.

Edited by SamBridge
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This video of the Coriolis effect at the equator and

at 8 feet on either side of the equator requires a

valid scientific explanation to what is going on here

concerning conservation of angular momentum

of the water draining from the sink on either

side of the equator.

 

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This video of the Coriolis effect at the equator and

at 8 feet on either side of the equator requires a

valid scientific explanation to what is going on here

concerning conservation of angular momentum

of the water draining from the sink on either

side of the equator.

 

 

Semjase,

 

you really need to learn to be more critical of your sources. People pulling this con are actually rather common in countries like Ecuador. The actual Coriolis effect on a tub of water that size is so tiny, that how a person breathes on the tank has just as much effect.

 

Typically what happens here is that a little bit of swirl is introduced by the act of moving the tub, as well as sitting the tank at a small angle. The con men are very good at putting right hand or left hand swirl in the tubs while moving them. And yes, that is enough to influence the direction the water will drain from the tub.

 

Again, the Corilois effect is pretty well understood. It is responsible for the direction of rotation for hurricanes. But for bodies that are much, much smaller than the radius of the Earth, the effect is truly negligible.

 

I'd suggest that you work through some of the mathematics yourself to prove this to yourself. It would be a lot more insightful than relying on YouTube videos for your evidence.

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A reporter from BBC went to the equator

and had the Coriolis effect tested for herself

in a draining funnel and found the same results

as the other video she said that even physicist

don't believe the results here's the report

 

http://news.bbc.co.uk/2/hi/programmes/fast_track/9758180.stm



Is the whole thing a fraud whats going on?

Edited by Semjase
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I'm fairly sure that the poles are the only two places that you won't get a Coriolis effect.

 

The poles are the two places where the Coriolis effect is strongest. There are a whole slew of places where you won't get a Coriolis effect: Anywhere on the equator will do.

 

 

This video of the Coriolis effect at the equator and

at 8 feet on either side of the equator requires a

valid scientific explanation to what is going on here

concerning conservation of angular momentum

of the water draining from the sink on either

side of the equator.

 

 

The scientific explanation is simple: It's a tourist scam. There is no Coriolis effect at the equator.

 

A reporter from BBC went to the equator

and had the Coriolis effect tested for herself

in a draining funnel and found the same results

as the other video she said that even physicist

don't believe the results here's the report

 

http://news.bbc.co.uk/2/hi/programmes/fast_track/9758180.stm

 

 

Is the whole thing a fraud whats going on?

 

On the reporter's part, it's just sheer stupidity. "Never attribute to malice that which is adequately explained by stupidity." (Hanlon's razor). This is not BBC's finest hour. The sad fact is that BBC has fallen for this scam multiple times. It's been debunked as a tourist scam, the BBC has been told that it's a tourist scam, and yet they still report it is something fantastic. It isn't.

 

On the part of the people demonstrating this fantastic effect: Yep. It's fraudulent.

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A reporter from BBC went to the equator

and had the Coriolis effect tested for herself

in a draining funnel and found the same results

as the other video she said that even physicist

don't believe the results here's the report

 

http://news.bbc.co.uk/2/hi/programmes/fast_track/9758180.stm

 

Is the whole thing a fraud whats going on?

 

Eric Idle or John Cleese (one of the Monty Pythons) hosted a short-lived science show on BBC not too long after the comedy troupe finished all their movies. Anyway, he fell for the rouse too. I remember this, because we actually used the clip of the show in a Philosophy of Science class to talk about how even on a science show, which presumably had several science professionals on staff, would still get caught up in the sensationalism

 

It was also where the teacher of the class showed us how the local pulled the trick off. Again, they are careful, but the guy would tilt the tub one way, and be sure to rotate it in a certain direction when turning to cross over the equator.

 

The point is, you can't just take these things at face value.

 

The reporter for the BBC, and all their fact-checkers should know better. But, mistakes get through all the time.

 

In you can't do the math yourself to show how the force is very teeny tiny, then I don't have many other ideas on how to show you that the Coriolis effect on a tub of water is negligible. Maybe you can help: tell us what it would take to convince you?

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Even wiki knows it's not the reason for baths draining clockwise/ counter clockwise

http://en.wikipedia.org/wiki/Coriolis_effect#Draining_in_bathtubs_and_toilets

 

If it were then it would require that the equator ran through the bathroom of the house I used to live in. The sink and bath drained in opposite directions.

 

So, in the world according to Semjase, the equator runs through a bathroom in the North West of England.

 

Even if it were true, it still wouldn't be a breach of the conservation of momentum, but an example of it.

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