Stringless Yo-Yo!

• Can you just like ... Yo-Yo like a basic Yo-Yo?
• Yeah, like this.
• But this is not a basic Yo-Yo.
• No!
• That is awesome! Nicely done!

This is Ben Conde, he's got a brand new channel on YouTube which is about Yo-Yoing like a crazy person. But, I'm going to figure out how this is possible. How this is possible with a string that's not connected to the Yo-Yo to get it to do all of these insane things. Wow! Gosh! How did you learn to do that? That's crazy!

Uh, just a lot of like lonely Saturday nights. So watch this motion here, there, and then you tug up.

• Yeah, you got it!
• (Derek Laughs) This is not gonna happen!
• You got it, dude! Pull up—ooooh, that was close! Tug up!
• Aww...
• Pull up! There you go!
• (Derek cheers)

So, how does this work? When the yo-yo is released, it unspools as it falls, gaining kinetic energy and rotational energy from the gravitational potential energy it had to start with. Yo-yos can spin really fast, around six thousand revolutions per minute. That's about as fast as most car engines can turn over, and this is important because it gives the yo-yo gyroscopic stability, which means its axis of rotation is maintained even if there's a breeze or some little disturbances.

Now, since the yo-yo has a lot of angular momentum, it continues spinning in the same direction, but when Ben tugs the string, he pulls it from one side of the yo-yo over to the other. So now, as the yo-yo continues spinning, it binds the string to the spool and starts to roll up the string. If you look closely at this shot, you can actually see the exact moment when the string binds to the spool, preventing the yo-yo from unraveling further and falling off the string.

That's all there is to it, yeah, there's no science behind it at all. To release the yo-yo, Ben throws it out and upwards without pulling back, so it completely unspools and continues spinning at the same high rate of rotation. But how does he catch it with just a string?

So, the way yo-yos actually do roll up is there's friction pads inside the yo-yo. These ones are made out of silicone. You see this like little gap inside? When that string goes inside, that creates friction, and while it's spinning, it rolls the yo-yo up. So if Ben can lodge the string in the gap of the yo-yo, it catches on the friction pads and the yo-yo starts to roll up the string again.

Even without the friction pads, when the string wraps around the axle, it creates a significant amount of friction in the same way that ropes wrapped around bollards hold big ships to their docks. The amount of tension a coiled rope or string can hold is given by the belt friction equation. This equation shows that the force the string can exert on the yo-yo increases exponentially with the angle the string makes around the axle. So even a few turns around the yo-yo allow Ben to pull it back into his hand.

(Derek): What is your favorite yo-yo moment?
My freestyle in 2011, the crowd stood up, and it felt good. It brought tears to my eyes, but I went back to my hotel room to cry 'cause I was happy. It was a good moment.

Hey, this episode of Veritasium was supported in part by Audible.com, a leading provider of audiobooks with hundreds of thousands of titles in all areas of literature, including fiction, nonfiction, and periodicals. And because Audible supports Veritasium, they give a special offer to anyone who watches this show. If you go to audible.com/veritasium, you can download and listen to any book for a one-month free trial.

The book I'm listening to at the moment is a classic of science fiction, it's Kurt Vonnegut's "Slaughterhouse-Five," an awesome book about becoming unstuck from time. It involves aliens and World War Two and kind of this weird time travel, but it's just a phenomenal piece of writing. So if you haven't read it or listened to it, you can check it out for one month free trial—just go to audible.com/veritasium.

I really want to thank Audible for supporting me, and I also want to thank Darren Dyke, who filmed the slow-motion shots in this video. He is phenomenal; that's why this video is so cool. And also, of course, Ben Conde, because he spent years of his life perfecting the skills that you saw demonstrated here. If you want to see more of him, you can go check out his channel; the link is in the description.

So again, I want to thank all of these people, and I want to thank you for watching.