Hey it's me Destin and welcome
back to smarter every day! I have a problem, there is a specific water phenomenon that I see happening all around me but I have no idea how it works I've been trying to figure it out for years, in fact i put a video on this channel in 2011, asking people to help me figure it out! there's something interesting happening here I don't understand it it looks like water droplets are standing on water droplets. It looks like water is hydrophobic it looks like when a bead of water skates across the hot griddle it creates a layer of water vapor underneath it only that's not what it is If you have any information please let me know I'd appreciate it you've seen this right? If you watch the world with a critical eye like I do you'll see this everywhere for example if you've ever allowed yourself to watch a drip coffeemaker when the conditions are just right you'll notice that coffee beads up on top of coffee what does it do that sometimes when you turn the shower head on the water will blast to the other side of the tub instead of making the bottom of the tub wet these pearls of water will dance on top of the water that's already in the bottom of the tub. Don't let this weird you out it's just water and food coloring but the interesting thing is if you get the stream in just the right location and interacts with a porcelain and the water that's in the toilet and just the right fashion you'll get these little drops that bead up. I don't understand what the conditions required to make it happen are, but I get really excited about it and I want to understand. Seriously one time we landed an Apache helicopter on the pad at work, and the environmental control system was leaking condensate down onto the asphalt, and the beads were happening there that was the moment I realized i have to know why this is happening. In order to figure it out we're going to Science Garage to see my friend Don Pettit who has out-of-this-world experience in the area of surface chemistry let's go get Smarter Every Day. its water dancing on water, but we're gonna do it here on earth, and then in space, that OK? Yeah, and we're going to water down this one! Yeah, and we're going to water down this one!
[laughs] that's bad. if you know who Don Pettit is you understand why I came to him it's rare to find a person that not only understands how to capture beautiful photos but also understands the fundamental science behind each image seriously who else do you know that collects books on surface chemistry and wedding phenomena you own these references? Yeah.
Really? Well I mean when you're into this kind of stuff you need it, right? Anyways scientists all over the world have created elaborate setups in their labs to try to observe these dancing drops and they've got some really great data but I knew if I got the right type of camera in Don's hands and just turned him loose we would not only get the data but we would do it beautifully it's a Phantom v2511 which is a very very fast camera and its really loud but we're gonna turn on the science here and give it a go after only about an hour of working through the lenses and lighting with Don, he quickly came up with a setup to observe a beautiful single drop of water landing on, bouncing, and then coalescing into a larger pool of water alright so we have a drop balancing on a still surface of water and you'll notice that it isn't coalescing. Coalescence is when you have two pieces of water that touch and then merge to become one piece. Now you notice there's this delay time where the drop is sitting there before coalescence that's called the 'Residence Time' tand scientists have a pretty good understanding of what's going on here. As a drop touches the surface scientists believe there's air trapped in-between as the drop rests that air starts to seep out of that gap and then coalescence occurs. The National Institute of Health did this really cool study where they verified the air gap theory by reducing the air pressure around coalescing water drops and as you'd expect the lower the air pressure to lower the residence time which is really cool anyway you can plainly see on the video that Don captured that as the drop comes to a rest it starts to slowly bob up and down and then it's like a little water bridge is built in that air gap and then coalescence occurs so this is my question in the phenomenon I'm seeing I'm seeing a steady state bouncing of a drop which means there's impacts happening over and over why is that not punching through that air gap and causing coalescence to happen easier? In order to understand this we actually have to look at that impact which means this is about to get awesome this is a device that's been shipped to me from another youtube channel Ben at NightHawkInLight and he has drops of water that he puts on water which is sitting in a speaker so we're about to basically recreate the setup that Ben did. So full disclosure you've done this in space right?
I have! But we're going to use this high-speed camera to understand the phenomenon here on earth and then you're going to teach me about what you discovered in space right?
Yeah we're gonna, we're gonna start on earth and end up in space [phone ringing] Hello?
Hey Ben it's Destin, how are you
Yeah and this is Don we're in science garage here having fun Awesome, Don it's cool to hear from you what frequency and amplitude worked out best for you? worked out best for you.
[Beep] if we were to turn that speaker off right now they would go away right?
Well let's see.
Okay See? They're there but they coalesce very quickly So, okay keep doing that don't change anything we'll change one variable OK.
That's me turning on the vibration of the speaker. So what I think is happening is; the water is trying to settle and go down and press against the surface Uh-huh that's right.
But because it's being pushed back up due to that vibration it, it adds energy back into the system and then pushes it away And I'm saying that that process keeps the small air gap between the drop, it helps maintain that You can sit here and postulate things
till you're blue in the face, until you make an observation to see what that fundamental physics is, then you can back out what's going on and high-speed of what's going on with that drop it would do a lot to help answer these questions this is quickly becoming one of the most awesome setups I've ever been a part of, would y'agree? Yeah this is just totally awesome. But you've been to space! Allright, here we are the moment of truth after years of waiting we finally have everything we need in order to make an actual observation. Here we go. and there it is did you see it? When i first saw this footage it stood out to me like a sore thumb instead of crashing into the drop like I anticipated it's almost like those peaks and valleys make some type of moving catcher's mitt that gently catches the drop and lets it down gently without breaking that air layer now i want to zoom in and see if we can see that wave catch the drop there it is it's pretty clear what's going on here think about it this way if somebody threw you a water balloon would you rush your hand up and try to meet it really quickly and risk bursting that surface tension? No, you would try to match the velocity of the balloon with your hands so you could decrease the collisional kinetic energy in fact there's an equation for how to calculate collisional kinetic energy and that's what factors into whether or not the drop survives if the velocity of the liquid and the small drop are about the same then that factor goes to 0 and the collisional kinetic energy quickly decreases to zero now that we understand this we can infer that timing is a huge factor here and there's probably a bunch of drops that just don't survive because they hit the wave wrong in fact that's exactly what we see in the high-speed. One more thing to think about is the fact that gravity is constantly pulling the drops back down to that vibrating surface which means it always has to find the soft spot to land the larger the drop, the greater the gravitational force pushing down on it. But what if you did this somewhere where there was no weight on the drop? Oh, then it bounces off I've got the video.
Can we see it? Yeah! I discovered this phenomenon for myself occurring naturally in the woods of alabama in 2011, the same year that Don Pettit launched to the international space station where he accidentally recreated the phenomenon in a really remarkable way. He performed a very similar water speaker experiment, except in weightlessness the water forms a sphere. Just to make it interesting Don put an air bubble on the inside of that water sphere and then he played tones through the speaker just to see what would happen [Don]... and the air bubble is attached
to the speaker cone, and so is the water and i'm at 60 Hertz i'm going to start increasing the amplitude, here we go Wow. So we're getting a series of standing nodes on the interface of the air bubble with the water. I'm going to put a square wave in OK... triangle wave So Don played with different frequencies, amplitudes, he played different types of music like rock and roll, and then he played the cello Don said whenever he played cello music specifically, little drops would break off on the inside of the sphere and start bouncing around on the inside. A Cello!? There's something about the Cello! [Music: Bach's Cello Suite No. 1 - Prelude] This video sets my brain. on. fire. We've learned two main mechanisms for coalescence we have the weight of the drop that squishes that air boundary and makes it go we have no weight, so we're left with collisional kinetic energy every collision that results in the coalescence, everything is right there and you can just directly see what's happening the sidewall that's vibrating? It makes the small drops go faster than the big drops, because there's lower mass but it's the same amount of excitation energy i really liked this video it's beautiful on multiple levels and I I want you to think it's beautiful too [Music: Bach Cello Suite 1] this has been a huge science goal for me for a really long time, so I want to say thankyou to the google making in science team for making this video possible thank you so much if you would seem really cool videos check out the hashtag #sciencegoals there's all kinds of videos being uploaded all the time for example check out Ben at NightHawkInLight, obviously he helped me make this video it was his speaker setup that helped us do the stable bouncing droplets in this video or check out Diana AKA PhysicsGirl who teaches you how to make anti-bubbles in your own home using household items or you can go check out this cool video by Derek at Veritasium who explains that the bouncing drop mechanism can be used to model quantum theory. He uses bouncing drops of silicone oil to reproduce the double-slit experiment check out any of these other videos under the hashtag #sciencegoals to go see really awesome science content A huge thank you to Don Pettit for sharing his knowledge of surface chemistry and his orbital footage in a really humble way that was awesome thank you Don! Last thing, the v2511 the Phantom that we used in this video that's now thing on smarta every day which has also been a science goal for a really long time so if you're interested in subscribing you've ever thought about it now is a really good time to do that because the slow mo is about to get slower it's about the higher resolution and it's about to get more fun. Feel free to click my face if you'd like to subscribe if not that's it. I'm Destin, you're getting smarter every day.
Have a good one.
Watch till the end. The Cello making the space water dance is incredible.
I don't think I have seen this in my life.
The slow-motion footage of the water droplet is so incredible it's almost unbelievable. It looks like a simulation. Well done Destin (and Don)!
Here's a gif I made of dat water bounce.
Edit: And here's a gif of the coalescence, and the droplet on resonating water
Amazing science content as always, excellent job u/mrpennywhistle!
In case anyone was wondering, the cello piece is the Prelude from the Cello Suite No. 1 in G major (BWV 1007) by J S Bach
"You've done this in space, haven't you?"
"I have... "
Very similar to the recent Veritasium video. Great content as always /u/mrpennywhistle
That cello footage gave me goosebumps. Great video!
I missed it, what was special about the composition of sound waves coming from the cello?