Water spinning

[sebbysteiny]

Here's a question that will separate the wits from the halfwits.

 

When I go to the Equator in say, Africa, there is a man with a bucket. When he unplugs it on one side of the equator (I can't remember which one) the water drains clockwise (and you can see a leaf rotating clockwise). When he goes to the other side, it rotates counter clockwise. And when he is at the equator, it drains straight downwards with no rotation at all.

 

The question is, why?

 

Quality point for THE FIRST correct answer.

[Janus]

Well, the standard answer is that it is due to the Coriolis effect, which is an apparent force that acts on objects as they move towards or away from the Equator. In reality, however,

For an obejct the size of a bucket, however, what you decribe just doesn't happen. The water is just as likely to spin clockwise or counter-clockwise no matter where you are with respect to the equator. The reason being that the Coriolis force acting on something that small is so weak that other factors have a much larger effect.

 

You really need something as big as a storm system for the Coriolis effect to become the over-riding factor.

[sebbysteiny]

For an obejct the size of a bucket, however, what you decribe just doesn't happen. The water is just as likely to spin clockwise or counter-clockwise no matter where you are with respect to the equator.

 

It did happen. I saw it. For that reason, no QP I'm afraid :cocktail:. It's got to be the first entirely correct answer.

[Qfwfq]

How far from the equator does the bucket get moved, and how well is the water let settle? Near the equator it would have to be very, very perfectly at rest with the ground befor the plug is pulled and this would have to occur without perturbing the water's angular momentum (unless it's some voodoo effect).

 

BTW, no matter how exactly it is at the equator, it will not drain straight downwards with no rotation at all. It would have to have a very exactly zero angular momentum, it's like trying to balance a pencil on it's point.

[ronthepon]

This'll shed some light.

 

http://answers.yahoo.com/question/index?qid=20060919180301AADOg2b

[Janus]

It did happen. I saw it. For that reason, no QP I'm afraid :sad:. It's got to be the first entirely correct answer.

 

Then it was a trick, and you really can't expect someone to give an explanation to a trick on such a sketchy description of it.

[sebbysteiny]

I'm sure almost everybody has seen the demonstration by those guys at the equator.

 

I have chosen my words carefully. The first person to correctly explain why what I and others have seen happens will get a quality point. So, 'the water rotates like that because .....' is the type of answer that gets a QP.

 

We should also try to limit google research :sad:.

[Tormod]

This was also covered in detail in the book "Bad Science" by Phil Plait (the guy behind the Bad Astronomy website).

[sebbysteiny]

This was also covered in detail in the book "Bad Science" by Phil Plait (the guy behind the Bad Astronomy website).

 

Your probably right. But the water rotates like that because ...

 

 

Don't go into a long mathematical description. Just a few statements giving the general concepts behind the phenomina and how they react to create the effect will be sufficient :sad:.

[eric l]

What these guys pretend to demonstrate is the "Coriolis effect", that is also known in meteorology. It makes winds turn clockwise around a high presure zone, and counterclockwise around a low pressure zone in the Northern hemisphere, and the other way around in the Southern hemisphere.

Compare two points, on the same meridien, in the Northern hemisphere.

Due to the rotation of the earth, the point closer to the Equator has a higher linear speed than a point farther away. Inertia makes that when an object (particle of air, drop of water) moves from South to North (in the Northern hemisphere) it will deviate to the right (because, looking on a map, its horizontal speed is higher).

Of course, in a bucket the difference in speed is hardly measurable, a slight twist on the bucket or a well placed dent in the bottom has a lot more effect.

But I must admit, if convincingly performed, it is a good show.

For more info : http://en.wikipedia.org/wiki/Coriolis_effect

[Janus]

Your probably right. But the water rotates like that because ...

 

 

Don't go into a long mathematical description. Just a few statements giving the general concepts behind the phenomina and how they react to create the effect will be sufficient :).

 

Again, without actually seeing it done, or a very detailed desciption of how it was done by someone that knows what to look for, it would just be a guess.

 

For example. You say you saw someone place a ball in their hand, and then when they opened the hand, it was gone. How was it done? Just off the top of my head, I can think of 4 different methods of sleight of hand that would accomplish that effect. Without seeing the trick, I have no way of telling which one he used.

 

The same goes with the bucket trick (And it is a trick).

 

As far as the actual Coriolis effect goes, it is caused by conservation of angular momentum.

[sebbysteiny]

What these guys pretend to demonstrate is the "Coriolis effect", that is also known in meteorology. It makes winds turn clockwise around a high presure zone, and counterclockwise around a low pressure zone in the Northern hemisphere, and the other way around in the Southern hemisphere.

Compare two points, on the same meridien, in the Northern hemisphere.

Due to the rotation of the earth, the point closer to the Equator has a higher linear speed than a point farther away. Inertia makes that when an object (particle of air, drop of water) moves from South to North (in the Northern hemisphere) it will deviate to the right (because, looking on a map, its horizontal speed is higher).

Of course, in a bucket the difference in speed is hardly measurable, a slight twist on the bucket or a well placed dent in the bottom has a lot more effect.

But I must admit, if convincingly performed, it is a good show.

For more info : http://en.wikipedia.org/wiki/Coriolis_effect

 

Congrats Eric for your first Quality point. Well deserved. It happens because the guy gives a slight almost unnoticable twist on the bucket making the leaf turn anti clockwise. This twist occurs not by a flick of the wrist but by turning his body holding the wrist still. Subtle and very convincing. The lie that he uses that it demonstrates the coriolis effect is total bollocks, but convincing bollocks, whose sole purpose is to give the guy from a 3rd world country a handsome tip. To be fair, it's well deserved and alot of people have fallen for it (including myself :)).

 

The actual coriolis force I thought occured because the centrifugal force resulting from rotation of the earth is not straight upwards away from the centre of the Earth. One gets the component pushing you up (making gravity seem less, and this force has a name but I can't remember it) and the coriolus force pushing you towards the equator. Of course both forces are infact phantom forces in that they are only forces as percieved by the rotating observer. But who cares? The point is, you got it.

 

Sorry Janus, you came in a close second. But ignoring the time issue, you didn't reveal the crucial detail that it was done by a subtle twist either from the wrist of from turning his body around. I didn't say this question was easy did I :hihi:. So although you are second, you are the weakest link and you leave this thread ...

 

with nothing. :hihi:

[sebbysteiny]

Hmm, strange. I gave Eric a QP and it didn't register as rep 1. What's up? I think the monitors need to get on the case here!!! QP to the first monitor who sorts it out. :hihi:

[Qfwfq]

Eric has much to be proud of, his rep power is still zero because of the way the system works. There's a difference between rep points and rep power.

 

Sorry Janus, you came in a close second. But ignoring the time issue, you didn't reveal the crucial detail that it was done by a subtle twist either from the wrist of from turning his body around.

But how could he, without having seen the guy doing it?

 

I had even asked you about how far North and South he moves the bucket and how long he let's the water settle, you answered naught. People here have said all the essential, the only difference was Eric using the keyword 'twist' but he said it as a general example, none of us knew exactly how the bucket was moved.

Not fair. :)