In “Paradolia,” filmmaker Susi Sie plays with pareidolia, our tendency to seek patterns in nebulous data — like faces on a slice of toast. Droplets of miscible and immiscible fluids collide, part, and mix in each sequence, providing plenty of fodder for an active imagination. For myself, my brain especially likes assigning cartoon expressions to well-spaced drops in the video. What do you see? (Video and image credit: S. Sie)
The roars of big cats — tigers, lions, jaguars, and leopards — carry long distances. In part, this reflects the animals’ size: large lungs exhale lots of air through a large voice-box, whose vibrations resonate in a large throat. But size alone does not make the roar. Below are examples of two big cat voice-boxes. On the left is the nonroaring snow leopard; on the right is the voice-box of a roaring jaguar. The red boxes labeled “VF” mark each cat’s vocal folds. Nonroaring cats have triangular folds, while roaring ones have thick square or rectangular vocal folds. These rectangular folds are more aerodynamically efficient, allowing them to produce a wider range of output levels. They’re also more resilient to the intense forces of a roar, thanks to the cushioning effect of fat deposits inside them. If interested, you can learn more over at Physics Today. (Image credit: tiger – T. Myburgh, voice box – E. Walsh and J. McGee; research credit: E. Walsh and J. McGee)
Icicles and stalactites grow little by little, each layer a testament to the object’s history. Here, researchers explore a similar phenomenon, grown from a dripping liquid. They’re called “flexicles” in homage to their natural counterparts, and they start from a thin layer of elastomer liquid. Though it begins as a liquid, elastomer solidifies over time.
To form flexicles, the researchers spread a layer of elastomer on an upside-down surface and allow gravity to do its thing (above). Thanks to the Rayleigh-Taylor instability, the dense elastomer forms a pattern of drips that, after hardening, creates a pebbled surface. Subsequent layers of elastomer will drip from the same spots as before, slowly growing longer flexicles (below). The team envisions using them for soft robotics, but, personally, I just really want poke at them and wiggle them. (Image and research credit: B. Venkateswaran et al.; via APS Physics)
Squeeze a bottle of cleaning spray, and the nozzle transforms a liquid jet into a spray of droplets. These droplets come in many sizes, and predicting them is difficult because the droplets’ size distribution depends on the details of how their parent liquid broke up. Shown above is a simplified experimental version of this, beginning with a jet of air striking a spherical water droplet on the far left. In less than 3 milliseconds, the droplet has flattened into a pancake shape. In another 4 milliseconds, the pancake has ballooned into a shape called a bag, made up of a thin, curved water sheet surrounded by a thicker rim. A mere 10 milliseconds after the jet and drop first meet, the liquid is now a spray of smaller droplets.
Researchers have found that the sizes of these final droplets depend on the balance between the airflow and the drop’s surface tension; these two factors determine how the drop breaks up, whether that’s rim first, bag first, or due to a collision between the bag and rim. (Image credit: I. Jackiw et al.; via APS Physics)
This astronaut photo shows Madagascar’s largest estuary, as of 2024. On the right side, the Betsiboka River flows northwest (right to left, in the image). Less than 100 years ago, most of the estuary was navigable by ships, but now more than half of it is taken up by the river delta. Upstream on the river, extensive logging and expansions to farmland have caused severe soil erosion; the river carries that sediment downstream, dyeing the waters reddish-orange. As the river branches and the flow slows, that sediment falls out of suspension, building up islands and seeding new sand bars further downstream.
In the image above, you can compare the 2024 delta to the way it looked in 1984. Letters A, B, C, and D mark the downstream-most islands from 1984. Today newer islands and sand bars sit even further downstream. (Image credit: NASA; via NASA Earth Observatory)
In 1181 CE, astronomers in China and Japan recorded a new, short-lived star in the constellation Cassiopeia. After burning for nearly six months, this historic supernova disappeared from the naked eye. It was only in 2013 that an amateur astronomer identified a nebula in the vicinity of that supernova, and, in the years since, astronomers have collected evidence that identifies the object, known as Pa 30, as the remnants of that 1181 supernova. Now, astronomers have mapped the supernova remnant, revealing an unusual dandelion-like structure (shown in an artist’s conception above and below). Filaments of sulfur project outward from a dusty central region that houses the remains of the original star. Normally, a supernova destroys its original star, but this was a Type Iax supernova, a “failed” explosion that left behind a hot, inflated star that may eventually cool into a white dwarf star.
Why the supernova remnant has this strange shape remains unclear. Scientists speculate that shock waves may have helped concentrate sulfur into these clumpy filaments. The material’s velocity suggests a ballistic trajectory (meaning, essentially, that it has neither sped up nor slowed down since the original explosion). Winding the trajectory backwards pegs their origin to 1181, helping confirm that Pa 30 is, indeed, the remains of that 1181 supernova. (Image and video credit: W.M. Keck Observatory/A. Makarenko; research credit: R. Fesen et al.; via Gizmodo)
In February 2024, the North Atlantic’s sea ice reached its furthest extent of the season, limning the coastline with tens of kilometers of ice. These images — both capturing the Labrador coast on the same day — show the swirling patterns marking the wispy edges of ice field. In this region, the ice is likely following an eddy in the ocean below. Eddies like these can form along the edges where warm and cold currents meet. An ice eddy is particularly special, though, as the water must be warm enough to fragment the sea ice, but not so warm that it melts the smaller ice pieces. (Image credit: top – NASA, lower – M. Garrison; via NASA Earth Observatory)
When millimeter-sized drops of water infused with nanoparticles dry, they leave behind complex and beautiful residues. As water continues evaporating, the residues warp, bend, and crack. In this video, researchers set their science to the music of Leonard Cohen. The results resemble blooming flowers and flying water fowl. If you’d like to learn more about the science behind the art, check out the two open-access papers linked below. (Video and image credit: P. Lilin and I. Bischofberger; submitted by Irmgard B.; see also P. Lilin and I. Bischofberger and P. Lilin et al.)
Artist Akiko Nakayama’s intuitive grasp of fluid dynamics is so good that she manipulates liquids live to musical accompaniment. Her dendritic paintings — made from a combination of acrylic paint and isopropyl alcohol — inspired scientific research papers. There’s no substitute, I’m sure, for seeing her art live, but you can get a taste of her performances in the video below. Then you can head over to Physics World for more on the artist, her inspirations, and her scientific collaborations. (Image credits: H. Akagi and A. Nakayama; video credit: Eternal Art Space; via Physics World)
The Earth’s inner core is a hot, solid iron-rich alloy surrounded by a cooler, liquid outer core. The convection and rotation in this outer core creates our magnetic fields, but those magnetic fields can, in turn, affect the liquid metal flowing inside the Earth. Most of our models for these planetary flows are simplified — dropping this feedback where the flow-induced magnetic field affects the flow.
The simplification used, the Taylor-Proudman theorem, assumes that in a rotating flow, the flow won’t cross certain boundaries. (To see this in action, check out this Taylor column video.) The trouble is, our measurements of the Earth’s actual interior flows don’t obey the theorem. Instead, they show flows crossing that imaginary boundary.
To explore this problem, researchers built a “Little Earth Experiment” that placed a rotating tank (representing the Earth’s inner and outer core) filled with a transparent, magnetically-active fluid inside a giant magnetic. This setup allowed researchers to demonstrate that, in planetary-like flows, the magnetic field can create flow across the Taylor-Proudman boundary. (Image credit: C. Finley et al.; research credit: A. Pothérat et al.; via APS Physics)