down the plughole

when the water seems to be rotating as it goes down the plughole is it the earth's rotation that you are seeing?
if so, why doesnt water rotate in an ordinary bowl?

Originally posted by eamon o
when the water seems to be rotating as it goes down the plughole is it the earth's rotation that you are seeing?
if so, why doesnt water rotate in an ordinary bowl?

It isn't... The Coriolis effect on flushing water is just a myth. Simply put it doesn't have enough intensity on the scale that the water movement is being made to actually have any influence in it.

Originally posted by adam warlock
It isn't... The Coriolis effect on flushing water is just a myth. Simply put it doesn't have enough intensity on the scale that the water movement is being made to actually have any influence in it.

so why does it go around?

Originally posted by eamon o
so why does it go around?

Next time wait a little bit after pouring some water. When you can discern no kind of agitation in the water just let it go through the plughole and try to inflict as less agitation as you can. If you do it carefully enough you'll be able to see the water go down with no turn around. If it was due to the earth's movement you'd always see the vortex.

The water turns around because when we fill the container with water, water molecules are bouncing all over and when we insert our hands we make a little bit more mess so when the water flows it flows down the drain with a circular motion. But I'm sure that if you see enough times going down the drain in the same sink you'll see it spinning in one direction and other times in the other direction.

Originally posted by eamon o
so why does it go around?

Because the bowl is designed to make it go around like that.

Originally posted by adam warlock
Next time wait a little bit after pouring some water. When you can discern no kind of agitation in the water just let it go through the plughole and try to inflict as less agitation as you can. If you do it carefully enough you'll be able to see the water go down with no turn around. If it was due to the earth's movement you'd always see the vortex.

...[text shortened]... e same sink you'll see it spinning in one direction and other times in the other direction.

You make it sound like it is simply a case of being able to see the motion already in the water. It is more than that. As the water comes towards the plug hole, unless it approaches it in a directly straight line, it experiences centrifugal force. All it takes is a tiny disturbance and before long there is guaranteed to be some rotation. Its hard to describe the whole thing in a post, but basically once it gets going, the rotation near the centre is the strongest and generates rotation further out, so once it starts going one way it will never switch unless you completely disturb it or intentionally rotate it the other way. Its a self feedback type of effect.

Originally posted by twhitehead
You make it sound like it is simply a case of being able to see the motion already in the water.

I tried to make it sound like it the fact of the water going drown the plughole with a circular motion and it's direction depends on the initial conditions and has nothing to do with the fact that the earth is rotating.

Originally posted by twhitehead
You make it sound like it is simply a case of being able to see the motion already in the water. It is more than that. As the water comes towards the plug hole, unless it approaches it in a directly straight line, it experiences centrifugal force. All it takes is a tiny disturbance and before long there is guaranteed to be some rotation. Its hard to descr ...[text shortened]... pletely disturb it or intentionally rotate it the other way. Its a self feedback type of effect.

By the way: would you consider joining Club 39?

Originally posted by adam warlock
By the way: would you consider joining Club 39?

Whats it about?

Originally posted by twhitehead
Whats it about?

A club to discuss topics in science (mainly physics and math) and more technical contributions are strongly welcomed.

It'll be a place for some discussion and mutual help. For instance if you know neat problem or a neat solution to a problem and want to tell us about it.

Check out this thread Thread 100130 to see what inspired me to this club.

The water spirals because the intensity of the flow rate causes a vortex....as Adam said, it has nothing to do with the Earth's rotation.

Regarding the coriolis effect (caused by the Earth's rotation), I heard that England kept missing to the wrong side during the Falklands war because they were correcting for a Northern hemisphere coriolis effect....then eventually realized their error.

Anyone else hear of that?

Originally posted by eamon o
when the water seems to be rotating as it goes down the plughole is it the earth's rotation that you are seeing?
if so, why doesnt water rotate in an ordinary bowl?

The reason you cannot see an ordinary (still) bowl of water rotate is because it rotates very slowly - at one revolution per day, and we are also rotating at that rate.

The flushing of water down a plughole amplifies the spinning effect of the earth (exactly the same as an iceskater pulling in their arms), of course it amplifies any other disturbance in the water as well, and any nonsymmetric flow pattern induced by a dented bowl. In reality, common disturbances such as that caused by the hand that pulls the plug, or the spin from the water being poured into the bowl not having settled yet, will tend to be more than 1 revolution per day and so will dominate the effect.

To g

Originally posted by flexmore
The reason you cannot see an ordinary (still) bowl of water rotate is because it rotates very slowly - at one revolution per day, and we are also rotating at that rate.

The flushing of water down a plughole amplifies the spinning effect of the earth (exactly the same as an iceskater pulling in their arms), of course it amplifies any other disturbance in ...[text shortened]... led yet, will tend to be more than 1 revolution per day and so will dominate the effect.

To g

So are you saying that the water rotates 1 revolution in relation to the bowl (per day) or 1 revolution together with the bowl (thus staying essentially stationary with regards to the bowl)?

Obviously your distance from the equator would make a significant difference to the effect. At 45% N for example the water is supposedly rotating at a 45% angle.