Hydrodynamic Levitation!
Check this out! Hahaha, isn't that awesome? That is hydrodynamic levitation. Check it out! This styrofoam ball is levitating on this stream of water, and it's doing so in a very stable way. The set up is so stable you can play Frisbee through it, which is weird to me because the water is off to one side of the ball. And that doesn't seem to make any sense, 'cause you can block the water for a second and the ball will still levitate. Have a look! Isn't that cool?
How can it be stable like this? How can this be a stable configuration? That is what we're gonna explain. This is my friend Blake. He is a toy inventor, and he actually came up with this, and he brought it to me. I was like, "That is awesome, there's some really cool physics going on here."
Juggling with water. I can't believe it will just allow you to switch balls like that. They can even hit each other as they go down. It doesn't take the other one off the stream. So how does this effect work? Well, a lot of people might think of the hairdryer ping-pong ball effect, which works basically based on Bernoulli's principle. That's actually what we're showing here. We've brought this stream down so it's going at a very low velocity. So it's pretty much laminar flow, and what you can see, if you look at the ball, is it's entirely enclosed in water, so that water stream comes up, goes around the ball.
And just as with the ping-pong ball, if it moves to one side of the stream, it slows down the flow of fluid, and according to Bernoulli's principle, this increases the pressure relative to the faster flowing fluid on the other side. So it pushes the ball back into the middle. That is what provides the stability for this ball. But I think what we're seeing with the bigger balls is something different.
This is the largest styrofoam ball I could find, so I don't expect it to work, but hey, we're gonna give it a shot! Should I go higher? Oh! It's happening! That is incredible! Look at it dance on there, man! It's like got this instability, but it corrects. It's incredible! You should see the way the water is spiraling off there. That is awesome!
So I've been thinking a lot about the physics that makes this possible. What I think is happening is as the stream contacts the ball, it pushes it up, but it also pushes the ball out, away from the stream. So what I think is remarkable is that the ball actually will stay there. It is in a stable configuration. From looking at the high-speed footage, what I really think is going on is this water is getting thrown over and down by the ball, and since the ball is putting a force over and down on the water, that water is putting a force up and in on the ball, which keeps it right in that stream.
It's because there's a bit of adhesion between the water here and the styrofoam. It starts to go a little slower, that pulls all that water over the ball. And that's the start of how you get the ball to spin and how you get that sprayed down on the right-hand side, which provides more lift and keeps forcing the ball back into the stream.
Come on, once the ball is levitating, it remains stable because if it drifts too far into the stream that decreases the flow of water around the ball, reducing the force pushing it into the stream. And if it drifts too far out, that increases the water flow over the ball, increasing the force pushing it back into the stream. That's what makes the equilibrium position so stable. Any slight perturbation creates a restoring force that moves the ball back to equilibrium.
The rotation, I think is also nice because that gives it that angular momentum, providing a little bit of stability side by side. That's not so important for these balls, but it certainly is important for the disc. If you try to levitate a disc, you need to keep it in the right orientation.
Oh, yes! Getting the discs to levitate is significantly harder than the balls because they have to maintain their vertical orientation in order for this to work. Even a slight breeze makes this very difficult.
HEY! Check that out! Can you come in and get it? Oh my goodness! This is a clear demonstration that that is not just about the Bernoulli effect, right? It's due to the rotation of the disc that actually carries the water over and sprays it down, which pushes that back into the stream. That's amazing!
Not only is this an awesome experiment, it's also pretty fun to play around with in the summer, and it was invented by my friend Blake. So come over to my channel, Innovinci, and I'll show you how, with a simple Home Depot run, you can build this in your own backyard. I'll put a link to that video right here. So if you want to make this, go check it out!