The Truth About Toilet Swirl - Southern Hemisphere

Today, we’re trying something that’s never been done before. I have made this video and Destin has made a video on Smarter Every Day, and we want you to play them both at the same time. So there’s a link to his video down in the description, so find a way to load both of these videos and then synchronize them on my mark.

In 5, 4, 3, 2, 1...

In Sydney, Australia, we are at 34 degrees South Latitude. Which is the opposite side of the world from Huntsville, Alabama. So, which way do the toilets flush? That is the question. The Simpsons did a whole episode based on toilets flushing the opposite direction in Australia. Plus, other shows have supposedly demonstrated this effect. So is this a real effect or not?

“The application of this principle to water draining in Earth's two hemispheres is just bunk.” If you try it yourself, you’ll find inconsistent results. This sink sometimes drains one way and sometimes the other way. In any container of water, there's always going to be some rotation. The water is not perfectly still. And it is this, rather than the hemisphere, that determines which way the water will swirl down the drain.

But what if we could eliminate all motion from the water? I have here a five foot wide kiddy pool. I actually filled the pool in the anticlockwise direction to be sure any clockwise motion we see is not due to how I filled the pool. I’ve left this water sitting here for 24 hours. So it seems like I've damped all of the motion from the filling. I really hope this works.

Destin, wish me luck! I'm about to pull the plug. 3... 2... 1... And the pool is draining, but you can't see any motion of the water just yet. To help us see where the water is flowing, I'm going to put some food colouring in on the four cardinal directions around the pool.

You can clearly see that the water is flowing clockwise in this direction, and that makes sense because that's how it should flow in the southern hemisphere due to the Earth's rotation. But you can see what a tiny little effect it is and what extraordinary lengths I had to go to to see this effect. So really, you're not going to see it in a bathtub or in a toilet or in a sink because there are other sources of angular momentum that totally wash out this effect.

The Coriolis effect. There you have it... It works! To understand how it works, imagine a pool with one edge touching the south pole. The pool is stationary relative to Earth, but every day it’s actually completing one full revolution. You can see the side of the pool furthest from the pole travels much farther every day than the side right next to the pole.

So the outer side of the pool is moving fastest towards the East, and as you get closer to the pole, the velocity decreases down to zero. Now imagine we drain the pool. Water from the far side is moving too fast relative to the drain, and so it gets out ahead, whereas water from near the pole is going too slow and so it lags behind. So when the water approaches the drain, it swirls clockwise.

And this is the reason cyclones swirl clockwise in the Southern Hemisphere. The higher pressure air rushes into the eye of the storm and, just like in our pool, swirls in the direction dictated by the hemisphere. And that’s the truth about toilet swirl. I definitely learned something, and if you did too, then you should share these videos with your friends. So you should subscribe to this guy. Subscribe to Destin, Smarter Every Day.

Okay. Ah, you're here! That's what we're gonna do. We are going to subscribe to Veritasium en masse because it's an awesome channel. Oh, oh look. Where is the subscribe button? But seriously, have you subscribed to Smarter Every Day yet? Destin has made some of the best videos on the internet, like the backwards bicycle, Prince Rupert's Drop, and what it looks like to get a tattoo in slow motion.

I've been friends with Destin for about three years, and I'm pretty much convinced that the man is superhuman. Not only does he run a remarkably successful YouTube channel, he also has a wife and four kids AND he has a full-time job. The man is literally a rocket scientist. And he's friends with astronauts, and when he asks them questions, they answer him from space.

"You are getting smarter every day." This man deserves your subscription. If you're not subscribed to him already, I don't know what you've been doing with your life, but go over to his channel right now and subscribe to Smarter Every Day, and trust me, you will thank me later.

And I want to thank you for watching. Y'know, we have been working on this collaboration for about three years, and it feels so good to have it finally out there in the world. I hope you enjoyed it as much as we enjoyed making it. All right, I'll see you next time.