Misconception: Toilet water spin clockwise in America and counter clockwise in Australia when flushed.
Actual facts: Only true for a perfectly symmetric toilet in a vacuum.
The sources of this myth lie in the prediction of a subtle theoretical observation called the Coriolis effect. Using the Coriolis effect it can be derived when no other forces act on the liquid other then gravity, it will spiral due to Earth’s movement, and the direction of the spiral reverses between hemispheres.
But what is the Coriolis effect?
Earth's rotation creates a curve in respect to a non rotating observer
The Coriolis effect is considered a fictitious force, but that doesn’t make it untrue. It means that it’s not an actual force, but a force like phenomenon which is derived from the fact that the system is spinning. It doesn’t mean it’s not real, it’s just not an energetic force. It can be mathematically handled as if it was a force, and therefor it’s convenient to refer to it as one.
To better understand the Coriolis effect we’ll walk through a thought experiment.
First, imagine the earth as a perfect sphere made entirely out of ice, with a sledge on the north pole. Now imagine someone giving that sledge a push strong enough for it to reach the equator. For simplicity’s sake we’ll neglect Earth’s curvature (though it doesn’t take a huge leap of logic to understand that all of the following arguments apply to a sphere as well as a plane). For a person standing on earth, the sledge seems to be going in a straight line. However, for an outside viewer not rotating with Earth (but still neglecting it’s curvature) - Earth’s rotation seems to curve the sledge’s track in the direction of Earth’s rotation.
Now let’s imagine the ice is neatly covered with golf balls. The balls aren’t packed together too tightly so they have freedom of movement, but they are abundant enough not to create gaps the sledge can fall through. Let’s try pushing the sledge down from the pole to the equator and follow it’s track. While it’s not very apparent at first, there’s a huge difference this time.
Cloud formation caused by the Coriolis effect in Iceland (notice it spirals couter clockwise)
When the earth rotates, it utilizes friction and gravity to make the golf balls go along for the ride. But since the friction is not perfect (the balls aren’t rooted to the ground), the balls actually move a tiny bit slower than the planet. While the gap is negligible when addressing each ball individually, the accumulating differences make the sledge curve against Earth’s rotation direction. This is where it gets interesting: to the observer on earth, the sledge seems to be curving in a certain direction, but to an outside observer it would seem to be rotating in the other direction. (Can’t it rotate in a different curve in the same direction, or not curve at all to the outside observer? Not really… figuring out why will be left as an exercise for the reader.)
Now, in order to latch our mental experiment onto reality, let’s imagine the golf balls, as well as the sledge itself, as any kind of object whatsoever. And the Planet as the Earth we know and love. The effect we imagined applies to any items not affixed to the ground, which lay on top of other items not affixed to the ground (like clouds riding air molecules).
And this relates to toilets… how?
Patience, I’m getting there…
Examining the Coriolis effect, scientists has made the observation that, since the rotation speed changes in respect to your proximity to the pole, there’s actually a symmetry, the matter closer to the pole has more energy, so the general direction of motion has a slight inclination towards the equator. Yet since the direction of the rotation is opposite for a boat going from the south pole and one going from the north pole, the effects of the Coriolis force should be opposite.
In what’s considered to be a stupendous demonstration of Newtonian mechanics, scientists filled a very large and very very precisely built bowl with a hole drilled almost exactly in it’s center. According to predictions, the waters did form a spiral, going counter clockwise on the north hemisphere and clockwise on the south.
So didn’t you just justify the myth instead of debunking it?
Not really. Remember, the bowl had to be very large and very precisely built.
For the Coriolis effect to be noticeable a few conditions need to be satisfied; the most relevant one is that if we draw any straight line which goes through the center of the (presumably round) draining hole of our toilet the mass of water on each side of the line would be identical. If it isn’t, the asymmetry would cause the water to spiral down the drain. But if we build an exact mirror image of the container (in respect to the line which exhibits the biggest mass difference) the water would spiral the other way around - independent of the hemisphere the container is on. This demonstrates the fact that simple calculations prove - the Coriolis effect is a few orders of magnitude smaller than other factors such as the geometrical shape of the container, the drain pipe’s tilt, surface winds and such. For such small amounts of water the Coriolis effect is so small it’s actually rendered negligible.
So yes, it’s technically possible to figure out what hemisphere you’re on using a bowl of water, but toilets? Well, they just aren’t accurate enough to be a reliable measurement device.
Next: Do advanced life forms have bigger genomes? Did modern society bring evolution to a halt? Have men evolved from monkeys? What is the purpose of evolution?
Some of my favorite misconceptions regarding evolution are going to be viciously exposed.
