Why Does Water Circle a Sink Hole?

[surabhi]

hi...

we see this phenomenon in our everyday lilfe...

in a sink, if we open its hole suddenly, the water gushes toward it in circular manner and not directly...

why the water has to first circle the hole and then it passes through the hole...why it never takes the shortest route to go through the hole...

pls clarify..

 

[tiny-tim]

welcome to pf!

hi surabhi! welcome to pf!

it depends which way you pull the plug out …

it's almost impossible to pull it out vertically or radially (ie without any clockwise our anticlockwise motion) …

so when you pull the plug, you're actually stirring the water by doing so …

the water will continue to flow down the plughole the way you stirred it!

 

[GT1]

hi surabhi! welcome to pf!

it depends which way you pull the plug out …

it's almost impossible to pull it out vertically or radially (ie without any clockwise our anticlockwise motion) …

so when you pull the plug, you're actually stirring the water by doing so …

the water will continue to flow down the plughole the way you stirred it!

So theoretically if I mechanically prevent the plug to rotate while pulled (press fit it to a guiding tube etc..) there won't be any vortex at the sink?

 

[JaredJames]

So theoretically if I mechanically prevent the plug to rotate while pulled (press fit it to a guiding tube etc..) there won't be any vortex at the sink?

I've never heard of this "we create the vortex when pulling the plug" idea, not sure how true it is.

The vortex created is one of the most efficient ways for water to travel down the hole.

If you take a 2 litre bottle, fill it with water and turn it upside down, it will glug out as the air is sucked in. If you do the same thing but rotate the bottle gently, you will create the vortex which will allow the water to empty smoothly whilst allowing the air in.

 

[tiny-tim]

I've never heard of this "we create the vortex when pulling the plug" idea, not sure how true it is.
…
If you do the same thing but rotate the bottle gently, you will create the vortex which will allow the water to empty smoothly whilst allowing the air in.

Exactly! You create the vortex by giving the water an initial rotation …

you decide whether it's clockwise or anti-clockwise!

 

[JaredJames]

Exactly! You create the vortex by giving the water an initial rotation …

you decide whether it's clockwise or anti-clockwise!

With a bottle yes, because I'm spinning it.

But I just spent ten minutes pulling the plug and couldn't change the direction of rotation as you describe.

I can understand how it may affect things, but my bathroom sink has a mechanical plug (you operate a lever to open the plug - no contact with it - the plug doesn't rotate at all when pulled) and the water still rotates.

 

[tiny-tim]

… my bathroom sink has a mechanical plug (you operate a lever to open the plug - no contact with it - the plug doesn't rotate at all when pulled) and the water still rotates.

since we're into experimental physics here …

does it rotate the same way every time? ​

(and does it make any difference whether you originally filled the sink from the left or the right tap/fawcet?)

 

[JaredJames]

does it rotate the same way every time?

No, this one actually surprised me. Mostly always went anti-clockwise but twice it went clockwise.

(and does it make any difference whether you originally filled the sink from the left or the right tap/fawcet?)

Central mixer tap directly over the plug.

I can't believe I'm doing this, what a way to spend a Saturday.

 

[tiny-tim]

No, this one actually surprised me. Mostly always went anti-clockwise but twice it went clockwise.

Central mixer tap directly over the plug.

Well, it certainly isn't trying to do straight down, and if it goes either way, then surely it must be the initial conditions?

I can't believe I'm doing this, what a way to spend a Saturday.

Could you possibly post a video of it?

And have you used a spirit-level to check that the sink is perfectly level?

 

[JaredJames]

Well, it certainly isn't trying to do straight down, and if it goes either way, then surely it must be the initial conditions?

Well it's what I'm inclined to think, but then what would change those conditions in a mechanical setup? I suppose I'm over thinking it, looking at the sink/drain design instead of your own motion.

Could you possibly post a video of it?

Yes, I'll immortalise my exciting home life.

And have you used a spirit-level to check that the sink is perfectly level?

I installed it, how dare you insinuate my handy work is shoddy!

 

[tiny-tim]

Well it's what I'm inclined to think, but then what would change those conditions in a mechanical setup? I suppose I'm over thinking it, looking at the sink/drain design instead of your own motion.

hmm … if the plug doesn't come up exactly straight (say if it leans slightly towards two o'clock), it will create a flow within the sink even before there's a hole …

since the sink isn't symmetric, that flow will be rotational

Yes, I'll immortalise my exciting home life.

just the bathroom, please …

leave your public wanting more, and you'll be able to bring out a sequel! …

maybe about whether the light goes out when you close the fridge?

I installed it, how dare you insinuate my handy work is shoddy!

even in Vegas, they re-check the equipment every day

oooh … if you set up a webcam, you can take bets on which way it will go next time! ​

 

[JaredJames]

hmm … if the plug doesn't come up exactly straight (say if it leans slightly towards two o'clock), it will create a flow within the sink even before there's a hole …

since the sink isn't symmetric, that flow will be rotational

That's what I'm thinking at the moment.

just the bathroom, please …

leave your public wanting more, and you'll be able to bring out a sequel! …

maybe about whether the light goes out when you close the fridge?

Just to re-enforce how exciting things are...

In my first year of uni we 'tested' this whilst a bit drunk. We emptied the fridge in the uni halls and one of my flat mates climbed in (small Chinese dude).

even in Vegas, they re-check the equipment every day

oooh … if you set up a webcam, you can take bets on which way it will go next time! ​

I like your thinking. There be money to made!

 

[tiny-tim]

Just to re-enforce how exciting things are...

In my first year of uni we 'tested' this whilst a bit drunk. We emptied the fridge in the uni halls and one of my flat mates climbed in (small Chinese dude).

Well, don't keep us on tenterhooks …

tell us the results! ​

(unless there's an embargo until the paper is published )

 

[Redbelly98]

I doubt that sinks and tubs can be made and oriented perfectly symmetric. There is bound to be either some sideways tilt, or groove-like angled imperfections, that cause the water to spin one way or another. In that case it will always go the same way for a particular sink or tub.