AMAZING underwater vortex rings!

Hey noise oh yeah vortex rings there's swirling masses of fluid smoke rings bubble rings sometimes made by dolphins sometimes tied in knots we'll get to those later but sometimes they're made by crazy youtubers hey I'm Diana and you're watching physics girl I want to make a vortex ring in the pool so my most popular video ever is of a half ring vortex we made in the pool so I recently wondered could we make a full vortex ring I know it can be done because we've already done it but even before we tried it I thought it could be done because we'd already made a half ring vortex in the pool remember with the plates you couldn't see the vortex at first but you could see the shadows made by the surface of the water where the vortex met the air and cause the water to dip down we won't be able to use that effect to help us see the ring if it's fully submerged underwater but we could try the food colouring thing which we did with the first half ring vortex by dropping food coloring into the ends and watching it travel down to illuminate a full half ring but for the full ring hmm there are no ends so we're gonna have to try to get the food coloring in there before it forms or as its forming I have an idea I had an idea so to show you what we did and then I'm gonna talk about these vortices in real research like knotted vortices tied in knots but first here's what we did in the pool being so kind at lending me his pool and also helping me thanks for your pool we have a vortex cannon which is usually used for air vortices and for shooting people but we're using it in the water and my idea is that I'm gonna squeeze some of the food coloring just on the outside in the front right where the vortex is coming out and hopefully they'll get sucked in and make a full rain for Tex more food coloring at Marvel guy okay try that oh I shot too far upwards all right [Music] [Music] [Music] [Music] [Music] [Music] so yeah it worked that was a lot of fun now how could we make vortex rings even cooler a vortex ring is just a vortex like any other swirling mass of fluid tornadoes water spouts dust devils whirlpools but with the vortex ring you take the vortex line which is the actual scientific term for the line that all of the fluid swirls about and you wrap it in a circle but you could wrap it in all different crazy shapes the only necessary condition is that the vortex line cannot end in a fluid and in any medium so obviously our half ring vortex line ended but it ended at the surface between the water and the air you wouldn't be able to make that half ring fully underwater it would either close or it would just dissipate breakup but interestingly vortex lines can end in fluids when they're forming or dissipating for example a vortex line created by an airplane engine can sometimes bend and stretch until it reaches the ground where physics will then allow it to end and stay there and you get weird looking phenomena like this so as long as the vortex line doesn't end in the fluid you can make really crazy shapes with the vortex and for a long time scientists wondered how to make vortices tied in knots which was hypothetically possible but practically a big challenge until William Irvine and his team came along I just have to ask are all the bottles on the shelf back there because you've had so many so bration successful graduations that's great we're scientists for a while trying to make knotted vortices so the history goes back a long ways actually goes back all the way to Lord Kelvin Lord Kelvin was in fact I think basically responsible for introducing the idea of topology in physics and knots and physics so there's some accounts of Lord Kelvin himself trying by colliding smoke rings basically all the naive approaches seem to fail and by naive approaches I mean sort of smashing vertices into each other hoping they will not up but the solution that we found would have been very very hard to do in practice before recent times 3d printing allows you to have a sort of rapid turnaround time and prototype and go from idea to experiment in in a day basically so we ended up piggybacking on a known fluid dynamics effect which is called the starting vortex airplanes have these trailing vortices behind them that's a sort of very very well known fact but what's less well-known is that the moment in which the airplane accelerates it actually emits a vortex that gets left behind and that vortex actually connects up with the trailing vortices and closes on the wings our idea was that we could use that effect in order to engineer vorticity in the lab essentially by 3d printing wings making them of the shape that we wanted so we made a vortex knot we made links rings here's an example of the wing that makes the link rings accelerating them and possibly hoping that then they would leave behind the vortex of the shape of