Travellers and Scientists please answer this. In which direction does the water go down your drain?

Question

I live south of the equator. When we drain the sink or the bath the water goes down the drain in a clockwise direction. I have always been told that if you are north of the equator it goes down in an anti-clockwise direction

Is this true?

And if you live right ON the equator what happens then??

Does it just go straight down??

And if it is true, how and why does the equator effect it??

Answer 1

<<Is this true?>>

The direction the water goes down a drain has nothing to do with which side of the equator you're on.  It depends upon how the sink and bath are built.  It's a widespread myth that's nevertheless wrong, and that's despite the elegant explanations offered to account for something that doesn't actually happen.

Answer 2

It is true, and it is because of a force differential.  The water going down on the side nearer to the equator is moving slightly faster than the other side, which determines the direction of the swirl.  

You can observe this by filling two pitchers of water, and pouring them into the sink at the same time from opposite directions.  

If you pour them from "3:00 and 9:00", the water hits, and does nothing special.

If you pour them from "2:00 and 8:00", the water will spiral anti-clockwise.

If you pour them from "4:00 and 10:00", the water will spiral clockwise.

As for right on the equator, that is practically impossible.  The differences between the forces are very small, and even if you were accurate to within 1mm, you'd still be off-center enough to swirl one way or the other.

It's like having kids pushing a carousel in opposite directions.  It would be nearly impossible, if everyone pushed as hard as they could, to balance the strength of 20 kids pushing in different directions so they would all cancel each other out.  Eventually, one side would have to win, and the carousel would move in that direction.

Answer 3

No, it's not true.

The direction the water spins in a drain is dependent on the construction of the sink and residual momentum in the molecules of the water.

You would need a sink at least 15 feet in diameter to have any chance of observing a coriolis effect (and probably more like 1,000 feet in anything but perfect laboratory conditions). It is true for things like hurricanes.

There is an effect similar to the Coriolis effect that is strongest at the equator. It is called the Eötvös effect, and pushes things up or down depending on whether they are traveling East or West.