When a test tube of liquid hits a surface, the curvature of the meniscus focuses the rebounding fluid into a jet. In this video, researchers show some of the many variations they’ve explored on these experiments–from changing the depth of the fluid and the shape of the container, to changing the working fluid to honey or to dry grains. It’s a nice introduction to a fascinating phenomenon! (Video and image credit: H. Watanabe et al.; research credit: H. Watanabe et al. and K. Kobayashi et al.)
In mechanical systems, gears and pulleys transmit rotation from one location to another. Here, researchers explore a fluid dynamical version of such systems. The set-up consists of two rotors contained in a cylindrical corral filled with a water-glycerin mixture. One of the rotors is active, marked here with orange; the other (blue) one is passive, meaning that it can rotate due to the forces on it but it is not actively driven by a motor.
The three flow visualizations illustrate different configurations the rotors can take on, depending on their separation distance. In the top image, the rotors have a moderate separation distance and the passive one rotates opposite of the active one. That rotation direction is set by the high-shear flow on its inner side. If the rotors are close together (left image), they rotate in the same direction, aided by strong shear on the outside edge of the passive rotor; this mimics being linked with a belt. And, finally, if the rotors are widely separated, they also corotate, with the fluid in between acting like a virtual gear linking them. (Image credit: J. Smith et al.)
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)