Heterochromia iridum is the formal name for when a person’s irises are multi-colored, often with streaks or swirls of one color cutting through another. In this short film, photographer Rus Khasanov recreates the effect with glittery inks and paints. Their varying surface tensions help create the eye-like streaks and feathers through the Marangoni effect. Check out the full video to see the effect in action. (Image and video credit: R. Khasanov; via Colossal)
Saturn’s rings are one of the most iconic sights in our solar system, and scientists are using them to learn more about the planet they surround. Until recently, scientists believed that gas giants like Saturn and Jupiter have dense, rocky cores buried beneath their gassy atmospheres. But a new study of Saturn’s rings suggests that Saturn’s core is far larger and more fluid than assumed.
When the interior of Saturn wobbles, it causes gravitational shifts that affect the material making up its rings. By studying disturbances in the ring system — a technique known as ring seismology — researchers can deduce what motions took place inside the planet to cause the changes in the rings.
Using data from the Cassini spacecraft, the authors determined that Saturn’s core likely spreads to nearly 60% of its radius, and, rather than being dense and rocky, the core is a relatively fluid mixture of ice, rock, and metallic fluids. The core diffuses gradually into the gaseous atmosphere, and it’s stably stratified against convection, so its wobbles are quite small for the planet’s size. (Image credit: rings – NASA; illustration – Caltech/R. Hurt; research credit: C. Mankovich and J. Fuller; via Gizmodo)
Few countries have to contend with water the way the Netherlands does. With 26% of its area and 21% of its population living below sea level, water control is critical. This satellite image shows some of the natural and manmade features that help protect the landscape. The West Frisian Islands, the long spine-like archipelago seen here, form the first barrier. Behind them lies the mudflats of the Wadden Sea, home to countless wetland species. The Wadden Sea is separated from the freshwater Lake Ijssel by the Afsluitdijk, constructed in 1932 to protect the country from rising seas. With the dam in place, the Dutch used wind power to drain the shallow lands behind the dam, reclaiming the polders labeled here. With the islands, mudflats, and lake between urban settlements and the sea, engineers have more options for diverting water and protecting people from disastrous flooding. (Image credit: A. Holmes/NASA’s Ocean Color Web; via NASA Earth Observatory)
Water droplets immersed in a mixture of oil and surfactants will move about, propelled by the Marangoni effect. Surfactant molecules congregate along the interface between the water and oil, but they do not do so uniformly. This uneven grouping causes variations in the surface tension, which in turn creates flows inside the droplet from areas of low surface tension to ones with higher surface tension. Those internal flows then dictate how the droplet as a whole moves.
Researchers found that droplet trajectories in these systems depend on the droplet’s size. Small droplets move in relatively straight lines, whereas larger droplets take highly curved paths. The difference comes from the way surfactants get distributed around the drop’s interface. Larger drops are more sensitive to shifts in surfactant location, making them more prone to take changeable, curving paths. (Image credits: top – P. Godfrey, others – S. Suda et al.; research credit: S. Suda et al.; via APS Physics)
Growing up in the Ozarks, I explored my fair share of caves and sinkholes. These geological features form when flowing groundwater erodes soil, sand, and even rock underground. The Ozark Plateau consists largely of limestone, which is water soluble, making it very prone to this internal erosion. As bedrock dissolves away, it is eventually unable to hold up the weight of ground above it, causing a catastrophic collapse into a sinkhole. Although my childhood sinkholes were naturally occurring, they can also form in spots where leaking pipes and infrastructure help wash underlying soil away. Unfortunately for engineers, this internal erosion can take place for years without any visible sign above ground. (Image and video credit: Practical Engineering)
The advantage of flying a drone over a volcanic eruption is getting all of the beauty with none of the danger. No asphyxiating on sulfuric gases, no burns from intense heat, no ash or flying rocks. Just the stunning, glowing beauty of fresh earth being born. “Stranded” takes us over and around the recent Icelandic eruption in a way that no human can ever experience. Sit back, relax, and feast your eyes on the spectacle. (Image and video credit: S. Ridard; via Colossal)
With their flexible, flattened shape, rays are some of the most efficient swimmers in the ocean. But, at first glance, it seems as if their protruding eyes and mouth would interfere with that streamlining. A new study uses computational fluid dynamics to tackle the effects of these protrusions on stingray hydrodynamics.
With their digital stingrays, the team found that the animal’s eyes and mouth created vortices that accelerated flow over the front of the ray and increased the pressure difference across its top and bottom surfaces. The result was better thrust and the ability to cruise at higher speeds. Overall, the ray’s eyes and mouth increased its hydrodynamic efficiency by more than 20.5% and 10.6%, respectively. The lesson here: looks can be deceiving when it comes to hydrodynamics! (Image credit: D. Clode; research credit: Q. Mao et al.)
Each winter millions of starlings migrate to Rome, where they form enormous murmurations in the sky above. The ephemeral and amorphous displays are driven by each bird responding to its neighbor’s motions. But the slight delay in individual responses gives the flock as a whole a wave-like, fluid appearance. Behaviors like this help protect the starlings from predators while they search out places to roost.
As neat as the displays are, though, they come with some real downsides, as the latter part of this video reveals. I don’t know about you, but I wouldn’t want to park my car outside in that storm! (Video credit: BBC Earth)
Anyone who’s dealt with hot glue guns is familiar with the long, thin tails of glue they leave behind. 3D printers suffer from a similar problem with the nozzle pulls away from viscoelastic materials like plastics and polymers. Little tails, like the ones seen above, are left behind on the part and must be cleaned away by hand. The source of the trouble is the elasticity of the fluid. Pulling on these liquids stretches them into long thin strands as the molecules inside the fluid resist. But researchers have found an alternate method to break the liquid cleanly: twisting.
When a viscoelastic liquid bridge gets twisted, the liquid undergoes what’s known as edge fracture, an elastic effect that creates an indentation that forces its way inward and breaks the bridge’s connection cleanly. Since the technique only requires spinning the 3D printer’s nozzle when detaching, it should be relatively easy for printer manufacturers to implement! (Image credit: 3D-print – T. Claes, illustration – H. Hill/Physics Today, animation – S. Chan et al.; research credit: S. Chan et al.; via Physics Today)
Fluid dynamics is a perfect subject for high-speed video. So much goes on at speeds that are far too quick for our eyes and brains to perceive. But there is such a thing as too slow – a concept explored in this Slow Mo Guys video, which takes everyday activities like turning on a faucet or splashing into a pool and slows them down a speed where one second lasts an hour. The video I’ve embedded here isn’t nearly that long; it speeds up and slows down. But if you really want to, you can watch Gav fall into a pool for a full hour. (Image and video credit: The Slow Mo Guys)