Wet fur forms a spiral of spiky hairs in this image by photographer Ben Dalgleish. For thin and flexible fibers like hair, a little moisture lets them clump together, forming stiffer (but still flexible) shapes. The technical term for this water-meets-flexible-solid phenomenon is elastocapillarity, and it lets you do things like wind a wire with a bubble. It also makes a big difference when washing hair, including in space. (Image credit: B. Dalgleish/BWPA; via Colossal)
Our ears, like those of many other animals, convert mechanical signals to electrical ones, through a Rube-Goldberg-esque series of transformations. External sound waves make their way down the soft tube of the ear canal, which funnels them to a thin-walled cone, the eardrum, that’s about half as large as a dime. Here, the vibrating air pushes against the cone’s membrane, and those vibrations travel onward through a linked trio of small bones that amplify the vibration’s amplitude.
The last of these bones presses against an even smaller, oval-shaped membrane. As the bone moves, it shakes the membrane, sending waves through the liquid on its other side. Those waves travel down the spirals of the tiny, pea-sized cochlea, named for a snail shell’s shape. As the waves move through the liquid, they bend bundles of hair-like strands back and forth, like tall grass waving in a breeze. The bending triggers a chemical that binds to nerves at the base of the bundles, sending an electrical signal through the nerve and into the brain.
But the hair-like bundles, known as stereocilia, are also able to amplify incoming vibrations. In this case, the bundles in the outer portion of the cochlea expend energy to bend more than the incoming vibrations naturally make them move. This bending amplifies the fluid motion that gets transmitted to stereocilia further down the line; it’s those bundles that will make the final conversion to an electrical signal the brain receives. (Image credit: B. Kachar; research credit: Y. Thipmaungprom et al.; via APS)
A sudden breeze can pluck droplets hanging from a stem. Here, researchers recreate that phenomenon in the laboratory. With a close-up view and high-speed images, we can enjoy every detail of the detachment and break-up. As the wire pulls away, it drags a liquid sheet off the droplet. The thicker rims on either side of the sheet eventually collide, creating a jet that stretches, deforms, and, at last, breaks. (Video and image credit: D. Maity et al.)
Fracture is a sudden, brittle breaking-apart that we generally associate with solid materials that get stressed too far. Some viscoelastic, non-Newtonian fluids have been known to fracture, but that was generally thought to be unusual. But a recent study turns that idea on its head, revealing that even simple, albeit highly viscous, liquids can fracture.
When you stretch a liquid, the general expectation is what you see above: the liquid gets drawn into an ever thinner shape. But researchers found that–when stretched quickly–that same simple hydrocarbon liquid cracked open:
There’s even an audible snap, which you can hear in the video below. The results were so surprising that they repeated the experiment several times and with different viscous (but Newtonian) liquids. The results held. When the liquids were pulled to a critical stress, they audibly snapped and fractured like a solid.
The next question, of course, is why this happens. The authors suspect (but have yet to show) that cavitation may be at play in the initiation of the crack that separates the liquid in two. (Image, video, and research credit: T. Lima et al.; via Gizmodo)
Over time, rivers naturally curve and meander. As water accelerates around a river bend’s curve, it creates a secondary flow that carves sediment away from the outer bank and deposits it on the inner one. That, in turn, makes the river bend sharper until it eventually cuts part of the river off into an oxbow lake. In this astronaut photo, we see the Alabama River flowing right-to-left. The river’s natural meander is constrained by the dam on the center left, which widens the river upstream. The higher water level upstream creates the feather-like floodplains lining the river. (Image credit: NASA; via NASA Earth Observatory)
Fabrics flutter in seemingly impossible ways in artist Thomas Jackson‘s images. But despite first appearances, each photograph is true to life; the fabrics are suspended on taut lines. Their dance is driven by wind energy, drag, tension, and flow–not manipulated pixels. I love the (turbulent) energy of them! (Image credit: T. Jackson; via Colossal)
In planetary atmospheres, energy and vorticity can cascade from large scales to smaller ones, but the mechanics of this transfer remain somewhat elusive. In a recent experiment, researchers built a lab-scale representation of an atmosphere using a meter-scale rotating annular tank. The outer bottom edge of the tank gets heated–representing the sun’s warming at the equator–while a pipe in the center of the tank gets cooled near the tank surface, which mimics the chilling effect of the poles. Researchers filled the tank with a water-glycerol mixture and recorded how their artificial atmosphere responded at different rotation rates.
The results show an energy spectrum that’s consistent with atmospheric observations–with a steep drop at large length scales and a flatter one at smaller scales. But interestingly, they also found that the cascade was temperature-dependent in ways that current models don’t predict. Untangling that effect could help us understand not only our atmosphere but those of other planets. (Image credit: tank – H. Scolan, animation – S. Ding et al.; research credit: S. Ding et al.; via APS)
On a vibrating fluid, droplets can bounce and interact in complex ways. Here, researchers demonstrate some of the peculiar dynamics of these wave-guided droplets, showing how they can do things like pair up in waltzes. To keep the droplets from coalescing with one another, they perform their experiments in a pressurized chamber; the higher air pressure makes it harder for the air film between droplets to drain during a collision, making the droplets unable to coalesce. Under these conditions, the authors show that the droplet-wave system has quantum-like statistics. (Video and image credit: J. Clampett et al.)
Flow visualization is both an art and science in fluid dynamics. Here, researchers were interested in studying the separation bubble that forms over a backward-facing ramp–a shape that shows up, for example, on an aircraft. In these areas, the flow over the surface separates, leaving an unsteady, recirculating bubble.
That’s the flow that researchers are visualizing here. They’ve done so by adding tiny helium-filled soap bubbles to the flow. With bright lights illuminating the bubbles, each one leaves a streak in a photograph, showing where the bubble moved during the time the camera’s shutter was open. Although images like these are beautiful, they can also be analyzed by computers to extract the underlying flow that created the image. (Image and research credit: B. Steinfurth et al.; see also here)
Peeking between the clouds, satellites caught a glimpse of a massive phytoplankton bloom off the coast of Greenland in May 2024. The tiny organisms may be visible only under a microscope, but gatherings like these stretch hundreds of kilometers and are visible from space. Like tracer particles in a flow, the phytoplankton outline the swirls and eddies of the underlying ocean. (Image credit: L. Dauphin; via NASA Earth Observatory)
