[rock music]

There's just something really satisfying

about skipping a rock.

If you ever skipped one five or six times

you might find yourself taking it a little more seriously.

See if you can get seven, eight, nine consecutive skips.

Turns out some people take stone skipping very seriously.

And actually compete to see who can skip the most

or who can skip the farthest.

[crowd cheers]

The current world record for most consecutive skips

is probably higher than you think.

Try counting the skips in this footage of the world record,

just don't blink.

Did you catch it?

That was 88 skips.

Here's the amazing thing.

Models actually project the limit

could be a lot higher than that.

Today we're gonna explore what that limit might be,

and why approaching or even exceeding it,

could be almost impossible.

To find out what it takes,

I skipped stones with the world record holder.

What was that, seven, eight?

You know, the odd thing is, I never count [laughs].

Are you serious, you never count?

I don't.

[Robbie] Talked fluid dynamics with a physicist.

It hits the water and this back end

sort of creates a wave, and so the stone tends

to rise up over that wave that it creates,

and that's what allows it to get a lift force

that gets it back in the air again

for the next impact, and over and over again.

[Robbie] And brought both of them together.

Oh. Oh.

Gorgeous.

To see if we can figure out

how a world-class stone skipper

gets so many touches on the water

and what the limit might actually be.

So we're here today with Kurt Steiner.

He's the world record holder in stone skipping,

specifically, most consecutive skips on the water,

and how many skips was that?

It was 88.

That's so remarkable, I can't even,

like, I'm not a really talented stone skipper,

but, you know, if I find myself at a lake with some stones,

I will do some skipping.

I think the most I've ever done is like 13 or 14,

and like, that makes me really, really happy and proud.

So 88 is like, how...

It is what makes you happy that counts more.

[Robbie laughs]

But I think we can get that number up a bit.

We flew Steiner and a couple boxes of rocks to Utah,

where he gave me some lessons on extreme stone skipping.

Steiner makes it look easy,

but a good skip is more than just how hard

you throw a stone or at which angle.

In fact, it all starts with the stone itself.

Okay, that was closer to like, 15, 16?

I was gonna say 15, yeah. All right.

15, all right.

So the most I've ever skipped before this,

Right.

Is around 14, 15. Right.

And here, on my second throw,

[chuckling] I hit around 14, 15,

which tells me there's a lot to do

with the rock you're using.

Steiner's stones made a huge difference.

The worst rock in this box Right.

Is better than the nicest rock I've ever skipped.

Steiner, like a lot of top skippers,

is very particular about his stones.

He collects his from Lake Erie,

a few hours from his home in Pennsylvania.

A lotta question as to what kinda rock is best, right?

The general category I use is just how many sides is it.

[Robbie] Steiner isn't just an expert stone skipper.

He's an expert stone picker, too.

[Kurt] This one is pretty similar

to the one I would've set the record with.

[Robbie] He uses different shapes for different skips

and different conditions.

People like triangles.

I use to like triangles

but they just chew up the water too much.

You're always kind of weighing

how much irregularity is in my rock

against how hard am I throwing it,

against what water am I throwing it onto.

[Robbie] Steiner also show me how to hold the stone

for maximum skipping.

The first thing you ever wanna do

is determine which side's gonna be down.

Mm-hmm. Right?

And you generally wanna go

with a flatter, or slightly rounded.

If it's cupped or jagged, put that up.

Especially you wanna look at the outer edge

because a stone almost never touches,

except around, the half inch around the edge.

[Robbie] But, as I soon found out,

there's a lot more to skipping

than just picking a good stone.

Oh. Okay.

[Robbie] Steiner uses a variety of grips and stances

for things like distance, power, and number of skips.

That's a high-spin throw,

and then there's one here

where you're a little closer to the water.

That's a good way to get a lotta power in real close.

[Kurt grunts] He's got a classic,

low, skimming toss and an unusual overhand swing.

But basically, you're just gonna try to swat the water

as hard as you can, with the rock as flat as possible.

[Kurt grunts]

[Robbie] He showed me how to get

a little more width on my skip.

Oops.

Lesson number one, throw hard.

You've got a lot more strength than you're usin.'

[Robbie] He suggested trailing my hand.

Yeah, and don't start pivoting your waist around

and your shoulder around

until that left leg is a good foot out in front of you.

If you drag your arm, right?

Right, you see what I mean?

You're almost opening up into the throw.

It'll tension up across here

and then essentially your hand is catching back up

to the rest of your body and will snap out better.

[Robbie] All right, let's give that a shot.

Okay.

Now that actually looked a little better to me.

So now the third part is where it comes together here.

That's where you gotta hit your target.

[Robbie] Next, Kurt had me aim

for a first touch closer to the shoreline.

Did you notice how, when you threw the rock,

the longer it stays in the air,

the more it'll roll over on it's side?

Mm-hmm.

That is always happening.

You can minimize that, obviously,

by lessening the time in the air,

which is one reason you wanna hit close.

So we're gonna be focusing on three things on this throw,

based on Kurt's feedback.

One, I'm gonna be delaying the start of my throw

so I can utilize more of my biomechanics.

Two, I'm gonna try to throw it hard,

and three, I'm gonna try to make contact

with the water really close to myself.

[Kurt] There it is.

[rock music]

So that looked like high teens to me.

Immediate, immediate improvement.

And that was your first try.

Yes! [laughing]

[chuckling] Yeah.

Yeah, yeah.

That's so cool.

It's every throw is a complete new puzzle.

So how is it that someone like Steiner

can skip stones so many times?

To find out, we asked Tadd Truscott,

who runs the Splash Lab at Utah State University in Logan.

Yeah, the Splash Lab, welcome.

[chuckling] Thanks.

You've got a lotta really cool stuff in here.

Yeah, it looks like junk but we're using all of it.

[Robbie] Yes, it's a real lab,

and the work they do there is amazing.

And then this tank here

where I shot bullets into it for my thesis, my Ph.D thesis.

You shot bullets into this?

[Tadd] Yeah, yeah, absolutely.

They were modified .22 bullets.

Is that what that hole is right there?

Yeah, yeah, it's where we missed.

But that's a misfire, but yeah.

[Robbie laughing]

[Robbie] To study stone skipping,

Truscott and his team recorded Steiner hurling stones

into a tank at thousands of frames per second.

To figure out how many skips are possible,

you have to first understand just how a skip works.

Here's what happens.

So you have the stone, it's in your hand,

and you throw it, and as you do that,

you release it off of your fingers,

and that causes it to have some spin.

So this spin is really important.

We call it gyroscopic stabilization.

It essentially holds the attack angle

of the rock with respect to, say, the surface of the water.

So then, when you hit the water, it deforms the water,

and pushes a wave out in front of it,

but the velocity of the stone is much faster

than the wave that it creates,

and so it ends up rising up on that wave that it created

and this causes a little lift force.

The rock is able to go back into the air and then back down.

And so this happens over and over and over again

for a good rock skip, right?

And that gyroscopic stabilization

is what keeps that attack angle correct,

and friction is really the only other thing

that's like reducing your ability to keep going.

[Robbie] The Splash Lab isn't the only one

studying stone skipping.

A group of French scientists first figured out a model

for ideal skipping in 2004.

These researchers in France found out

that the optimal angle for a disk

to skip on the water surface is about 20 degrees,

for both the attack angle and also that velocity vector.

That, coupled with, you know, how fast it is thrown

as well as how much gyroscopic stabilization it has,

sorta set up the problem to find out

what the maximum number of skips you can get,

or the number of skips you can get,

based on what that spin rate is,

and what that velocity is, and that impact angle.

[Robbie] Now you might think that studying stone skipping

is a bit frivolous

but Truscott says there are practical applications.

Yeah, definitely.

So a spacecraft that was proposed

that would bounce off the atmosphere

as it kinda came back towards Earth.

[spacecraft engine roaring]

And use that to keep itself out.

You know, if you wanna land on, say, the moon of Titan,

you may wanna come in for a soft landing.

Knowing how skipping works might be a great way to do that.

[Robbie] To figure out how Steiner skips so many times,

Truscott and his lab also went into the field

to gather data on his arm speed

and the rotation of the stones.

All right!

[laughing] I think that was it, dude.

[Robbie] Steiner's maximum speed

is around 50 miles an hour.

His world-record skip was calculated at 43 miles per hour,

but he also has years of experience.

Even his dud throws put my best efforts to shame,

but could someone best his record?

I've seen one or two people who have a technique

that could maybe beat that,

but it's almost impossible.

[laughing]

[Robbie] Now you might remember

from our previous episode on the fast ball

that pitchers are about maxed out on speed

at just over 100 miles per hour.

Truscott applied that metric to stone skipping

and came up with some amazing calculations.

Baseball.

A really safe place on our chart

puts you around 93-mile-an-hour throw

because these are a little heavier than a baseball,

and they're a little, they have a bigger radius,

which makes their moment of inertia larger,

so you need a little more energy in that side of it.

So 93 miles an hour is about where you're topping out.

You're gonna have

about 2,800 to 3,000 revolutions per minute,

and, if you can get there,

that's close to 164 joules,

you're gonna probably get close to 300, 350 skips.

[Robbie] 350 skips?

Under, yeah, under the current idea, yeah.

Is that even possible?

[laughing] 300 already just seems ridiculous, right?

I don't even know who could count that.

Like I couldn't count 10 today.

[Robbie] Steiner thinks the limit

is probably closer to 200.

That's what the number says, I'd like to go test it.

[Robbie] Truscott and other scientists

have modeled their projections

using a perfectly round disk, but, as Steiner showed me,

there are no uniform stones.

[Kurt] Because Mother Nature never sees fit

to make two of the same thing.

[laughing] I have to get on her about that.

[Robbie] So skipping a stone might seem

like a simple thing,

but it's actually this beautifully complex mix

of skill, athleticism, and fascinating physics.

It's such a miracle to me what's goin' on.

You know, it's this weird dance of water,

[Robbie] and stone, and air. So will we ever see

300 consecutive skips, or 350?

That's a good question.

It'll probably take someone with a major-league caliber arm

and Kurt Steiner's devotion.

But what we're seeing these days

from the world's top skippers is already almost impossible.

[rock music]