FYFD

Year: 2024

  • Featured Video Play Icon

    The Shape of Rain

    In our collective imagination, a raindrop is pendant shaped, wide at the bottom and pointed at the top. But, in fact, a falling raindrop experiences much more complicated shapes. Here, researchers blow a jet of air onto a still droplet, a good facsimile for a raindrop falling through the atmosphere. The jet of air first squishes the drop, then inflates it into a shape known as a bag. The thin sides of the bag stretch and eventually break, spraying tiny droplets. As the disintegration continues, the thick rim of the bag breaks up into big droplets. As the video demonstrates, viscosity and viscoelasticity can affect the break-up, too. (Image and video credit: I. Jackiw and N. Ashgriz)

  • Jamming Soft Grains

    Jamming Soft Grains

    Hard granular materials — sand, gravel, glass beads, and so on — can flow, but, in narrow regions or under large forces, they can also jam up, essentially turning into a solid. Soft particles can also flow and jam, but do so under different conditions than hard particles. One group of researchers used a custom-built rheometer to measure jamming in soft particles like the hydrogel beads pictured here. They found that they could extend existing models for jamming in hard particles, but they had to rescale the mathematics to account for the way soft particles change their shape under pressure. (Image credit: Girl with red hat; research credit: F. Tapia et al.; via APS Physics)

  • Martian Auroras

    Martian Auroras

    Auroras happen when energetic particles — usually from the solar wind — interact with the atmosphere. Here on Earth, they’re most often found near the poles, where our strong global magnetic field converges, funneling particles down from space. Our neighbor Mars has no global magnetic field. Instead, its magnetic field is a hybrid of two sources: 1) induced magnetism from electric currents in the ionosphere and 2) patches of magnetized iron-rich crust. Together, they form an uneven and changeable field that deflects the solar wind less than one Mars radius above the planet’s surface. In contrast, Earth deflects the solar wind about 10-20 Earth radii away.

    Discrete auroras (left panel) occur when electrons plunge down into the atmosphere on magnetic lines coming from Mars’ patchy crust. Global diffuse auroras (center panel) are caused by energetic solar storms that light up the whole atmosphere, sometimes for days at a time. In proton auroras (right panel), incoming solar protons steal electrons from native Martian hydrogen to form high-energy hydrogen atoms that cannot be magnetically deflected. Instead, they penetrate the planet’s bow shock and plunge into the atmosphere, creating a daytime aurora. (Image credit: UAE Space Agency/EMM/EMUS and NASA/MAVEN/IUVS; via Physics Today)

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    “Ink In The Water. Mix One.”

    In this ASMR video, black ink diffuses in water. When the video starts, the ink is so diffuse that it’s not apparent the video is playing backward. It’s only as specific structures — things like Rayleigh-Taylor instabilities, plumes, and jets — coalesce from the background that we recognize the time reversal. Though it’s probably unintentional, this makes for a neat, subtle commentary on the nature of isotropic turbulence. (Video and image credit: Wryfield Lab)

  • Water Suspected Beneath Mars

    Water Suspected Beneath Mars

    The surface features of Mars — crossed by river deltas and sedimentary deposits — indicate a watery past. Where that water went after the planet lost its atmosphere 3 – 4 billion years ago is an open question. But a new study suggests that quite a bit of that water moved underground rather than escaping to space.

    The research team analyzed seismic data from the Mars InSight Lander. Marsquakes and meteor strikes on the Red Planet send seismic waves through the planet’s interior. The waves’ speed and other characteristics change as they pass through different materials, and by comparing different waves picked up from the same originating source, scientists can back out what the waves passed through on the way to the detector. In this case, the team concluded that the data best fit a layer of water-filled fractured igneous rock 11.5 – 20 kilometers below the surface. They estimate that the water trapped in this subsurface layer is enough to cover the surface of the planet in a 1 – 2 kilometer deep ocean. (Image credit: NASA/JPL-Caltech; research credit: V. Wright et al.; via Physics World)

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    Breaking Down a Water-Powered Timer

    In his latest “cutaway” video, Steve Mould takes a look at how you can nest siphons to create a system that periodically flushes itself. This kind of water-powered timer is useful in, say, public restrooms with a urinal system that collectively flushes every once in a while. In the video, Mould talks through each step of the system and some of the challenges he ran into when trying to create a pseudo-2D version of it. As is often the case with these videos, it’s a strangely satisfying process to watch. (Video and image credit: S. Mould)

  • Shaped Splashes

    Shaped Splashes

    When a raindrop hits a leaf, it spreads out into a rimmed sheet that breaks up into droplets. These tiny drops can carry dust, spores, and even pathogens as they fly off. But many leaves aren’t smooth-edged; instead they have serrations or teeth. How does that affect a splash? That’s the question at the heart of today’s study.

    A water drop hits a star-shaped pillar and breaks up.
    A water drop hits a star-shaped pillar and breaks up.

    To simplify from a leaf’s shape, the team studied water dropping onto star-shaped pillars. As seen above and below, the pillar’s edge shaped the splash sheet, with the sheet extending further in the edge’s troughs. This asymmetry extends into the rim also, concentrating the liquid — and the subsequent spray of droplets — along lines that extend from the edge’s troughs and peaks.

    A viscous water-glycerol drop hits a star-shaped pillar, spreads, and breaks into droplets.
    A viscous water-glycerol drop hits a star-shaped pillar, spreads, and breaks into droplets.

    The team found that, in addition to sending drops along a preferred direction, the shaped edge made the droplets larger and faster than a smooth edge did. (Image and research credit: T. Bauer and T. Gilet)

  • A Triangular Prominence

    A Triangular Prominence

    Our Sun is a maelstrom of light and heat, a constant battlefield for plasma and magnetic fields. This recent prominence, captured by Andrea Vanoni and others, bore a striking triangular shape. This fiery outburst — larger than our entire planet — formed and broke up over the course of a single day. The wavy solar surface features in the lower part of the image are solar fibrils, magnetically confined tubes of hot plasma. What changing magnetic fields might allow them to burst forth in a glorious candle of their own? (Image credit: A. Vanoni; via APOD)

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    “Starlit”

    In “Starlit,” filmmaker Roman de Giuli leverages paint, ink, water, and oil to create astronomical views. Colorful droplets spin past like neon exoplanets. Shards of glitter form comets. Satellite droplets become moons about their larger sibling. (Video and image credit: R. de Giuli)

  • Catching Krill With Bubble Nets

    Catching Krill With Bubble Nets

    On their own and in groups, some humpback whales enclose their prey in bubbly columns before feeding. The whales build these bubble nets intentionally, swimming in a ring at a constant speed while producing bursts of air from their blowhole. After observing hundreds of bubble nets created by dozens of whales, researchers concluded that whales actively tune the nets, using more rings, closer bubble spacing, or deeper extents to suit their needs. Once they’ve completed the net, whales lunge up through the center, mouth open, collecting their food.

    In their study, the team found that building bubble nets is no more energy intensive for whales than typical lunge-feeding. However, the prey concentration in a bubble net means that hunting there nabs more food per lunge. The authors argue that the way humpback whales build and use bubble nets qualifies them as tool users on par with many fellow mammals, as well as some birds, fish, and insects. (Image credit: C. Le Duc; research credit: A. Szabo et al.; via Gizmodo)