Using electromagnetism, researchers are bending and shaping soft liquid wires even against gravity. The team used galinstan — an alloy of gallium, indium, and tin that remains liquid at room temperature. On its own, galinstan has a high surface tension and forms droplets. But with a voltage applied, that surface tension is suppressed, making the liquid form a long, thin, still-liquid wire. Adding a magnetic field allowed the researchers to manipulate the falling stream of liquid, even levitating loops of the metal against the force of gravity! (Image, video, and research credit: Y. He et al.; via Cosmos; submitted by Kam-Yung Soh)
Some people fly with geese to train them for wind tunnel tests, and some people fly with them to teach them safer migratory paths. Today’s video focuses on the latter, specifically conservationist Christian Moullec, who has spent decades living and flying with lesser white-fronted geese as part of an effort to save the threatened species. He flies with them using an ultralight aircraft, exercising daily to prepare for the cross-continental migration. To help fund the effort, he offers passengers a spot on his short flights, letting people fly with the birds! (Image and video credit: T. Scott; via Colossal)
In nature, objects like asteroids, black holes, and atomic nuclei can get distorted when spinning rapidly. Researchers are exploring these objects using a new model platform: particle raftslevitated by sound. The individual particles are less than a millimeter wide and tend to clump together due to the scattering of sound waves off neighboring particles. This effect provides a cohesive force — similar to surface tension or the effects of gravity — that draws the particles together. With the right frequency, the sound waves can also make the granular rafts spin, setting up a tug-of-war between cohesion and centrifugal force.
Using sound waves for levitation, particles slowly rise and clump together. Particles are approximately 190 micrometers each, and the video is drastically slowed down from real-time.
As the rafts spin, they distort, pull apart, and come back together. Interestingly, the cohesive force a raft experiences increases with the raft’s size. That makes the attractive force unlike surface tension (which is the same whether you have a bucket of water or a lake) and more like gravity (which is stronger with more material.) Because of this size dependence, the team hopes their granular rafts could be a new way to study the formation of rubble-pile asteroids and similarly granular systems.
As the raft’s rotation increases, it’s pulled apart by centrifugal forces, but the pieces later reconnect. Video is slowed down by a factor of 60.
Sewage systems rely on gravity to remove waste from our homes and carry it toward treatment plants. But that constant downward slope can’t always be maintained. Sometimes we have to bring the sewage back up to the surface to process it. For that, modern systems rely on pumps and other equipment to move the challenging slurry of liquid and solid materials. In this video, Grady from Practical Engineering breaks down the physics and engineering of sewage pumping. (Image and video credit: Practical Engineering)
In this short film by Vadim Sherbakov, macro shots of glittery ink and pigments look like astronomical vistas. The title of the film, “Velocity,” is spot on; every shot is full of flow and motion driven by the mixture of ink, alcohol, soap, and other fluids. That means lots of surface-tension-driven flow, and the glitter particles act as excellent tracers, giving a real sense of depth and direction for our gaze to follow. Watching films like this, I always want to pull out some odds and ends and try it for myself, but I’m certain my results would pale in comparison! (Video and image credit: V. Sherbakov; via Colossal)
A word of warning: today’s post includes visuals of digestion taking place in (non-human) embryonic intestines.
Our bodies rely on waves driven by muscle contractions to move both fluids and solids, whether through the esophagus, the ureter, the fallopian tubes, or the intestines. In areas where mixing is unnecessary, those waves move in a single direction, transporting the contents one-way. But in the intestines, mixing is critical to enhancing nutrient absorption, so mammal intestines have wave trains that move both forwards and backwards.
The majority of waves move downstream, carrying waste toward its exit (Images 1 and 2). But occasionally, upstream waves collide with their downstream counterparts to force material together, both mixing and delaying progress in order to allow better nutrient uptake along the intestinal walls (Image 3). (Image credits: top – S. Bughdaryan, others – R. Amedzrovi Agbesi and N. Chavalier; research credit: R. Amedzrovi Agbesi and N. Chavalier; via APS Physics)
Local topography in the Sea of Okhotsk funnels water to create some of the largest diurnal tides in the world — nearly 14 meters! The currents rushing past islands and outcrops create swirling vortices like the ones seen in this natural-color satellite image. In some places, you can even see multiple vortices, strung together into a von Karman vortex street. At high tide, the vortex streets stretch westward, but at low tide they point east. (Image credit: N. Kuring/NASA/USGS; via NASA Earth Observatory)
When birds come in for a landing, they pitch back and heave their wings as they come to a stop in a perching maneuver. Some birds, researchers noticed, partially fold their wings during the move, creating what’s known as a swept wing. Curious as to the effect of this sweep, the team recreated the wing motion of a perching bird using two flat plates — one rectangular and one swept — and measured the flow around them during the maneuver. They found that the swept wing had greater lift, thanks to a spanwise flow inherent to swept wings that helped stabilize the leading-edge vortex. (Image credit: D. George; research credit: D. Adhikari et al.; via APS Physics)
As oil slides down two slowly converging wires, the droplets will merge into a sheet that stretches between both wires. When this happens can vary somewhat but occurs somewhere around the liquid’s capillary length.
In the poster above, the leftmost image (not the illustration) shows three possible merger points. To the right of the image, is a teal curve; this is a probability density function. Essentially, this curve shows where the merger is most likely to occur. The peak of the curve corresponds to the most probable point of merger.
The following two composite images show the same system — same oil flow rate, same wire spacing — with gas blowing upward along the wires. As the gas’s flow rate increase, the oil drops get larger, making the oil films thinner. The result? The wires have to get closer to one another before the oil merges. That’s reflected in the yellow and orange probability density functions, which have peaks further along the wires than the no-gas-flow case. (Image credit: C. Wagstaff et al.)
From the right vantage point, an approaching dust storm — known as a haboob — can look downright apocalyptic. In this compilation of clips a decade in the making, photographer Mike Olbinski shows these storms in all their terrifying majesty. I love seeing how the cloud front overhead densifies as the dust below advances. Without these wide perspectives, it’s hard to appreciate an approaching haboob. When one blew through Denver a few years ago, I never saw it coming. My first clue was the tree in front of my office window whipping wildly back and forth just before the sky turned brown! I much prefer Olbinski’s versions. Congratulations, Mike, on a decade of haboob-chasing! (Image and video credit: M. Olbinski; submitted by jpshoer)
