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As a SciShow viewer, you can  keep building your STEM skills with a 30 day free trial and 20% off an annual premium subscription  at Brilliant.org/SciShow. 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. You’ll get a free 30 day trial and 20% off an annual premium Brilliant subscription.

From us at SciShow, we hope  you enjoy the exploration. [OUTRO]