natural phenomenon

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

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

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

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

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

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

JaredJames

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

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

No, this one actually surprised me. Mostly always went anti-clockwise but twice it went clockwise.
Central mixer tap directly over the plug.

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

tiny-tim

Well, it certainly isn't trying to do straight down, and if it goes either way, then surely it must be the initial conditions?
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'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.
Yes, I'll immortalise my exciting home life.
I installed it, how dare you insinuate my handy work is shoddy!

tiny-tim

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
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?
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

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

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).
I like your thinking. There be money to made!

tiny-tim

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.