Water spinning anticlockwise down the plug hole - Is it really an urban myth?

Question

I've always believed that water tends to spin in the opposite direction down a bath or sink plug hole in the southern hemisphere. I've recently been told that this is an urban myth and it makes no difference. I can't afford to fly to Australia to check, so can anyone tell me the truth?

Answer 1

Water does not swirl in any particular direction ANYWHERE, at least not due to the Coriolis force (i.e. the rotation of the Earth). That's because the Coriolis force that is acting on the draining water is *tiny*. And that's a good thing; if there was a strong Coriolis force we'd fel it anytime we moved, and it would be nauseating. You'd feel like you had been on too many amusement park rides, all the time.

Water draining down a sink does tend to spiral. It has a certain, small, net rotational energy while it's sitting there swirling around in the basin. As it drains, that angular momentum is focused on the water in the middle, and a vortex forms. But that vortex is due to turbulence in the water from pouring, or air currents, or uneven temperatures -- not to the rotation of Earth.

If you carefully observe drain spirals, I predict you'll see about as many clockwise as anti-clockwise vortices. Try it out.

Answer 2

I was fascinated by this as a child and have followed many a story with interest.

Fact:

the Coriolis effect creates cyclonic motion in rising or falling fluid masses.

the effect is opposite between the northern and southern hemispheres

the force is very small but constant

Question:
Are there any other sources of rotational motion in your sink or tube?

If there are no other forces (symmetric basin) and the water is allowed to sit until all residual eddies have dissipated, the tendency will be to follow the Coriolis force.

Note most toilets are designed to create a vortex. Do the American Standard toilets in the US take advantage of the Coriolis force???

It is a really weak force.

Answer 3

Try this experiment in your own sink:
1. Plug the drain.
2. Stir the water clockwise.
3. While the water is still moving, unplug the drain.
4. Observe the water draining.
5. Repeat stirring water counterclockwise.
6. Draw your own conclusions.

Answer 4

MYTH!!!

"Not only is the Earth's rotation too weak to affect the direction of water flowing in a drain, tests you can easily perform in a few washrooms will show that water whirlpools both ways depending on the sink's structure, not the hemisphere."

Answer 5

Sorry mate it's a myth. I used to be a plumber, it's down to the drain trap under the sink or bath. It's impossible to make the down pipe perfectly level so the down ward force imposed as the water is drawn into the drain will take the most direct route to the outlet.

Answer 6

I once asked a bunch of people via an email list I was on to go check a drain in the house, and tell me which way it drains. Quite a few people reported. They were all northern hemisphere people, but slightly more than half (14 to 12) drained counterclockwise (the "wrong" way).

Answer 7

Yes it is a myth. It only works with very large bodies of water like the oceans or the atmosphere. I you did a test over a period of time you would discover that it is quite random with your plug-hole. BTW... I am in Australia but I am not discussing my plug-hole. My plug-hole is strictly my own business.......

Answer 8

Plughole Vortex

Answer 9

The Coriolis force (responsible for the "spinning") is very weak. It is strong enough to affect hurricanes and cyclones, but not nearly strong enough to affect water going down a drain. That is a result of the angle the drain makes with the basin.

Answer 10

I have seen it go in both directions in several places all my life. Gotta be a myth, unless I've witnesses every exception known to man lol