Welcome back to Smarter Every Day.

Here's the deal. I've created a video in the northern hemisphere

and Derek from Veritasium has created one in the south.

You have to synchronize these two videos in order for this to make any sense

but it's totally worth it if you do.

So click the first link in the video description,

get the video ready, and then synchronize on my mark.

You ready?

5.. 4.. 3.. 2.. 1..

Video.

[toilet flush]

[music]

Here in Huntsville Alabama we're at 34 degrees north latitude.

- And we're gonna find out if the water swirls the opposite way here to how it does in the southern hemisphere.

- We're making the definitive video to settle this once and for all.

[whispers] It's never been done on the internet. You're gonna learn something.

[toilet flush]

So I have seen documentaries that seem to indicate that which hemisphere you're in determines which way the water is gonna swirl,

but there's this other group of people and they seem really confident that it doesn't matter where you're at, the water's gonna swirl however it wants.

But have you ever just looked for yourself and figured out which way your toilet swirls?

Here is Alabama I've noticed that some turn counter-clockwise, and some go clockwise.

You see most toilets have little jets in it,

so the swirl direction is determined by the design of the toilet and not which hemisphere you're in.

So it's a myth.

Crossing the equator does not mean the toilet's gonna change directions.

But what if we come into the garage and do a more controlled experiment?

This is a one and a half meter kiddy pool.

Instead of filling the pool with no vorticity at all I'm going against the way it's supposed to drain.

So I'm trying to fill it with the flow going clockwise.

So let's let the water settle for a complete day so that we know that it's perfectly still.

I'm not gonna reach in and pull the plug out because that would induce some vorticity.

I'm gonna use this valve that I have connected to the bottom of the pool.

Good luck Derek.

OK opening the valve in 3.. 2.. 1..

Water should be flowing.

OK water's been flowing for a couple of minutes and I haven't seen anything yet

so we're gonna put some dye in it.

Check it out, it's like a tornado, like right off the bat.

We've got a counter-clockwise rotation.

We filled it up clockwise and now it's going counter-clockwise.

We have a kiddy pool in my garage and the whole earth is rotating,

and the water is going counter-clockwise,

because I'm in the northern hemisphere.

It's real! This is real.

We just proved it because we just eliminated variables.

The coriolis effect is real!

Think about a pool near the north pole.

The earth is spinning on its axis so the pool spins around the pole once a day.

The whole pool is moving but the part that's closest to the equator has more momentum

and the part that's closest to the pole has less.

Think about these velocities relative to the drain in the middle.

When we pull the plug, all the water starts moving towards the middle.

The side nearest the equator is going faster, so that water outruns the drain,

but the water nearest the pole is going slower so it falls behind.

So when the water approaches the drain, it swirls counter-clockwise.

This is the reason hurricanes swirl counter-clockwise in the northern hemisphere.

The center of the hurricane has lower pressure just like a drain,

so the hurricane swirls just like our pool.

And that's the truth about toilet swirl.

That was awesome. What'd you think?

It's the first internet experiment from two different locations.

Pretty cool stuff, but you..

- So..

- Nope.

Subscribe to Derek.

I'm gonna actually go to his channel and make sure that you end up over there.

Let's go to Veritasium, invade it and subscribe it. Let's go, here we go.

- Oh hey, these are some of my subscribers.

I am so glad to see you here.

While you're here subscribe to Destin's channel.

This is a good looking channel.

I like your logo.

That's.. I like what you've got going on over here.

- OK I hope you enjoyed this really interesting collaborative episode of Smarter Every Day.

I want to thank 100% Derek Muller, Dr Derek Muller of Veritasium.

- Thank you Destin.

- No, so here's the deal. Seriously.

We came up with this three years ago.

- No lie.

- No lie, three years ago at YouTube headquarters we decided we were gonna collaborate.

Derek did his version almost immediately.

- Two years ago.

- Two years ago, so it only took him a year.

It took me.. Derek basically had to fly to Alabama to help me do it. [laughs]

- It's like if I don't come here, this is never gonna get done.

- Alright so Derek flew to Alabama and we.. here we are, preparing this pool in the middle of the night.

So, what I'm trying to tell you is, I want you to go to Derek's channel and subscribe.

This is a very hard push.

Go to Veritasium, subscribe to Veritasium.

He does all kinds of physics stuff.

It's really cool, you will enjoy it.

I'm telling you that right now.

We've been friends for a really long time.

Our channels are about the same size.

Just.. You should be subscribed to Veritasium.

So I will suggest that to you now. Just click on Derek.

- Click on my face.

- Click on his face, do that.

And.. you ready to drain this pool?

- Let's drain this pool.

- I think it's been three years.

- I've been waiting three years to drain this pool.

- [laughs] Go subscribe to Veritasium. I'm Destin, you're getting Smarter Every Day.

Have a good one.