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The world-record holder at skipping rocks kinda sucks at skipping rocks.
So do you, and so does everybody.
Not to come screaming in with a hot take about a relaxing outdoor
pastime with zero stakes, but it’s true.
Because while the world record is 88 skips in a row,
researchers predict we should be able to do hundreds. But we can’t.
And in our quest to understand why,
researchers have uncovered some real-world applications,
including bringing astronauts safely back from space!
[INTRO]
I’m pretty stoked if I get more than three skips,
so 88 seems unfathomable.
But from what we know of the physics behind rock skipping,
it’s very possible.
The throw itself involves two things: speed and angles.
First, imagine the throw.
The stone has to be traveling quickly in order to have
enough momentum to keep going after making contact with the water.
And it’s not just traveling really fast in a straight line.
The stone is angled slightly in order to collide with the water.
On top of that, the stone needs to be rotating,
which you accomplish by holding the stone with
your forefinger on the leading edge as you throw.
This rotation is part of the key to success because it gives
the stone stability as it flies through the air.
As the stone collides with the water,
there are a couple of forces acting on it.
The water pushes up on the moving stone as it makes an impact,
causing the stone to skip.
The collision also causes the water itself to move, creating ripples.
These ripples will add some drag and slow its momentum.
You’ll notice that as the stone begins to lose momentum,
it starts skipping more frequently, and the height of the skips
decrease until all of a sudden the fun is over.
Fun fact: Professional skippers call those frequent skips a “pitty-pat.”
So, if the goal is to maximize your skips
and get somewhere in the same ballpark as the world record,
you have to do a few things to overcome the forces acting on the stone.
You need to pick a flat, lightweight stone so the upward force of the water
is greater than the weight of the stone–
otherwise, it will just sink as soon as it hits.
And in a 2004 Nature paper– yes, a Nature paper about skipping stones–
the authors identify the magic angle of attack when throwing your stone.
They found that using a 20-degree angle in relation to the surface of
the water maximizes the number of skips and minimizes the amount of
energy lost, keeping the stone skipping longer.
Even with all of the forces acting against the stone,
models like this say we could create even more skips.
At this point, the writing team would like to apologize
for being bad at math and not being able to calculate
what the maximum number should be,
but they did find one expert who suggested
more than 300 skips should be fair game under ideal conditions.
But why is this so hard to put into practice?
First, it’s really hard to throw fast, with spin,
while at the same time being very accurate
and hitting the magic angle of attack.
At that point you’re talking Major League Baseball pitcher
levels of power and precision, and most pitchers
don’t moonlight as stone skippers.
But even if you could achieve that combination,
there are a lot of other factors working against you.
For one thing, Mother Nature didn’t make all stones
perfectly flat and round discs.
And researchers say that the best skipping stones aren’t stones at all.
If you could, you’d use something a bit squishy that deforms
as it connects with the water. Like a rubber ball.
But that would be littering, so don’t do that!
Also, most models simplify the real-world environment,
neglecting things like wind and waves,
all of which act against the stone.
So while way more than 88 skips could be possible,
in reality, there are too many factors that are out of our control
to make that happen without the help of
a controlled environment and maybe a robot!
But, in the pursuit of trying to understand skipping stone physics,
researchers have found some real-world applications.
For example, a skipping technique was applied to the Orion capsule
that landed in December 2022.
This was the first successful uncrewed mission of
NASA’s Artemis program, which will one day use Orion
to take humans farther than they’ve ever traveled into space.
When Orion was heading back to Earth,
it skipped off our atmosphere before re-entry.
It’s not quite the same as a stone skipping on the surface of the water,
but it did dip in and out of Earth’s atmosphere as
it changed its trajectory to intersect with Earth.
This move accomplished a number of things.
It helped the spacecraft land more accurately
so the crew could be recovered in a more precise location.
It also helped slow the speed of the spacecraft–
in the same way the water does when a stone skips on it–
while also reducing the amount of heat
being generated by the high-speed entrance.
While Orion was the first to successfully skip across Earth’s atmosphere,
the Apollo missions also had the capability,
though not the confidence, to use this strategy.
They did, however, inspire the application of this technique to
the Orion mission in order to make the journey safer for the crew aboard.
Spacecraft re-entry is only one thing we’ve been able to learn about
thanks to the physics behind a simple game.
But sometimes it’s fun to learn a little more
about an afternoon out by the lake, too.
Skipping stones is a lot harder than it seems.
After all, if energy-momentum conservation
is as reliable as the fancy physicists say it is,
you should be able to throw a little stone as far as the eye can see.
To learn more about energy-momentum conservation,
you can go to Brilliant.org/SciShow!
Their course on Special Relativity provides a full explanation
from a Penn State University PhD in physics!
It was even turned into a YouTube video series on MinutePhysics!
And we know how much you love YouTube videos.
That’s the kind of engaging stuff you’ll find in Brilliant’s courses.
They don’t just teach you what you want to know.
They do it the way you want to learn.
And once you’ve completed the 18 lessons in Special Relativity,
you’ll be ready to tackle Quantum Objects and Gravitational Physics.
So you’ll never run out of mind-bending topics.
You can head to Brilliant.org/SciShow or click the link
in the description down below to get started.
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From us at SciShow, we hope you enjoy the exploration.
[OUTRO]