FYFD

Category: Phenomena

  • Mushy Layers

    Mushy Layers

    In many geophysical and metallurgical processes, there is a stage with a porous layer of liquid-infused solid known as a mushy layer. Such layers form in sea ice, in cooling metals, and even in the depths of our mantle. Within the mushy layer, temperature, density, and concentration can vary dramatically from one location to another.

    The image above shows a mushy layer made from a mixture of water and ammonium chloride. Above the mushy layer, green plumes drift upward, carrying lighter fluid. Look closely within the mushy layer and you’ll see narrow channels feeding up to the surface. These are known as chimneys. In sea ice, chimneys like these carry salty brine out of the ice and into the seawater, increasing its salinity. See this Physics Today article for more details on the dynamics of mushy layers. (Image credit: J. Kyselica; via Physics Today)

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    Conserving the Hill House

    In 1904, Scottish architect Charles Rennie Mackintosh created the Hill House, a masterpiece of modern design decades ahead of its time. Unfortunately, the Portland cement used for the house’s exterior has not held up well to a century of Scottish rains. As water saturated the cement, it began to dissolve and crumble. So to save the property, conservators commissioned the giant chainmail Box that currently surrounds the house. It protects the house from rain while allowing ventilation that dries the house out slowly. As an added bonus, the superstructure allows visitors to appreciate the house from new angles. (Video credit: T. Scott; via Colossal)

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    Vortex Arms

    A fixed cylinder will shed alternating vortices in its wake, but one allowed to oscillate forward and backward in the flow instead sheds simultaneous vortices. The shape of the wake still depends on the flow’s velocity. At low flow speeds, the two vortices are the same size when they shed. At higher velocities, the two vortices still shed simultaneously, but one will be large while the other is small. The larger vortex moves faster and travels downstream, but the smaller, slower vortex drifts inward. In the next shedding cycle, the small and large vortices switch positions, creating alternating symmetric shedding. (Image and video credit: P. Boersma et al.)

  • Ship Tracks in the Sky

    Ship Tracks in the Sky

    Line-like clouds criss-cross the Pacific Ocean in this satellite image. Each one is a ship track, a remnant left behind a passing ship. As they travel, ships leave a trail of exhaust that seeds the atmosphere with aerosols that serve as additional nucleation sites for clouds. The tiny particles interact with existing low-level clouds, making them brighter. Of course, the aerosols are present in the wake of ships regardless of whether they seed clouds that we can observe. (Image credit: J. Stevens; via NASA Earth Observatory)

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    Backflipping Bubbles

    Rising bubbles can backflip when they impact a tilted surface. As shown in this video, small bubbles will bounce off a titled surface, with each hop leading the bubble further up the incline. For slightly larger bubbles, though, things get a little more complicated. The bubble impacts the surface, bounces away, then circles back and makes its second impact behind the first before moving further up the plate. What drives this backflip? The researchers found that circulation around these bubbles is asymmetric, generating a lift force that drives the bubble’s backflip. (Image and video credit: A. Hooshanginejad et al.)

  • Rocked By Waves

    Rocked By Waves

    This astronaut photo shows the Isles of Scilly off the Cornish coast. The pale turquoise waters mark shallow reefs and shoals between the islands while blues reveal deeper waters surrounding the isles. The sun angle is perfect for highlighting the complex wave patterns caused by the winds and tides. Look closely and you’ll see swells intersecting one another and even diffracting around the smaller islets. (Image credit: NASA; via NASA Earth Observatory)

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    Butterflies Emerging

    When a butterfly emerges from its chrysalis, it flaps its wings to help pump fluids through its body, essentially inflating its new adult form. You get a glimpse of that process here in this Ant Lab video, along with some spectacular slow motion footage of butterflies taking off. I’m always amazed to see how much butterfly wings flex with each wing beat! Even more impressive is the strength of the insect’s lift; as seen here, a butterfly is strong enough to take off while supporting both itself and a mated insect. (Image and video credit: Ant Lab/A. Smith)

  • Streaks of Sea Ice

    Streaks of Sea Ice

    As summer approaches in the Southern Ocean, sea ice melts, but the process is not purely one-way. Temperatures in some locations are cold enough for some limited new freezing. The result is a mix of ice conditions like those seen here. The oldest, thickest ice is part of the ice shelf in the image’s lower right. Normally, younger sea ice would nestle against this shelf, but strong winds have blown that ice north-eastward.

    In the open waters between, delicate frazil ice — tiny needle-like crystals — forms. The wind, coupled with the wave motion, drives the frazil ice together to form streaks of nilas, which eventually accumulate into a layer along the older, broken, windswept ice. (Image credit: J. Stevens/USGS; via NASA Earth Observatory)

  • Beijing 2022: Sliding on Snow

    Beijing 2022: Sliding on Snow

    Skiing and snowboarding events rely on the peculiar physics of sliding on snow. According to classical lubrication theory, that sliding shouldn’t be nearly as low in friction as what we observe. The key here is that snow is soft and porous; it’s compressible, but it can also trap air (or water) in the pores between flakes. Because the passage of a skier or snowboarder is so fast, the air doesn’t have the time to slip out of the pores. Instead, it gets pressurized, providing lift that keeps the slider’s friction low. In the end, it isn’t the snow holding the slider up, it’s the air trapped in the snow beneath them! (Image credit: skier in powder – J. Andersson, snowboarder – Visit Almaty, halfpipe – P. T’Kindt; research credit: Z. Zhu et al.)

  • Beijing 2022: Monobob

    Beijing 2022: Monobob

    Bobsleigh, as a discipline, has been dominated in recent years by teams seeking every aerodynamic advantage to shave hundredths of a second off their runs. So it’s fascinating that the newest event in the discipline — the women-only monobob — cuts away that secretive part of the sport by permitting sleds from only one manufacturer. Every athlete competes in an identical sled. Not only that, they swap sleds between runs based on their times! So the fastest athlete from the first run will switch sleds with whomever had the slowest time.

    The event’s rules refocus the competition on athletic performance and skill rather than incentivizing countries who can afford to spend more money on wind tunnel testing and F1 design companies. That’s a great step toward leveling the playing field. I can’t wait to watch! (Image credit: OIS)