FYFD

Category: Phenomena

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    Manu Jumping, a.k.a. How to Make a Big Splash

    The Māori people of Aotearoa New Zealand compete in manu jumping to create the biggest splash. Here’s a fun example. In this video, researchers break down the physics of the move and how it creates an enormous splash. There are two main components — the V-shaped tuck and the underwater motion. At impact, jumpers use a relatively tight V-shape; the researchers found that a 45-degree angle works well at high impact speeds. This initiates the jumper’s cavity. Then, as they descend, the jumper unfolds, using their upper body to tear open a larger underwater cavity, which increases the size of the rebounding jet that forms the splash. To really maximize the splash, jumpers can aim to have their cavity pinch-off (or close) as deep underwater as possible. (Video and image credit: P. Rohilla et al.)

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    How Insects Fly in the Rain

    Getting caught in the rain is annoying for us but has the potential to be deadly for smaller creatures like insects. So how do they survive a deluge? First, they don’t resist a raindrop, and second, they have the kinds of surfaces water likes to roll or bounce off. The key to this second ability is micro- and nanoscale roughness. Surfaces like butterfly wings, water strider feet, and leaf surfaces contain lots of tiny gaps where air gets caught. Water’s cohesion — its attraction to itself — is large enough that water drops won’t squeeze into these tiny spaces. Instead, like the ball it resembles, a water drop slides or bounces away. (Video and image credit: Be Smart)

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  • The Hidden Beauty in the Mundane

    The Hidden Beauty in the Mundane

    Physicist Sidney Nagel has spent his career on topics that are somewhat unexpected: how coffee stains form, how droplets splash — or don’t, and how fluid flows into viscous fingers. Often this means looking at the mechanics of everyday occurrences that we otherwise take for granted. Instead, Nagel probes carefully at things like a coffee stain, asking why it’s darker at the edges and what he could do to keep that from happening — all to ultimately uncover the forces and mechanisms at play. Quanta has a great little interview with him on this and other topics. Check it out here. (Image credit: S. Nagel and K. Norman; via Quanta)

    Images of droplets breaking off.
    Assorted "coffee-ring" stains, where particles collect toward the contact line along the circumference of the drop.
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    Bigger Particles Slide Farther

    Mudslides and avalanches typically carry debris of many shapes and sizes. To understand how debris size affects flows like these, researchers use simplified, laboratory-scale experiments like this one. Here, researchers mix a slurry of silicone oil and glass particles of roughly two sizes. The red particles are larger; the blue ones smaller. Sitting in a cup, the mixture tends to separate, with red particles sinking faster to form the bottom layer and smaller blue particles collecting on top. And what happens when such a mixture flows down an incline? The smaller blue particles tend to settle out sooner, leaving the larger red particles in suspension as they flow downstream. (Video and image credit: S. Burnett et al.)

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    Fractal Fingers

    As bizarre as the branching fractal fingers of the Saffman-Taylor instability look, they’re quite a common phenomenon. In his video, Steve Mould demonstrates how to make them by sandwiching a viscous liquid like school glue between two acrylic sheets and then pulling them apart. The more formal lab-version of this is the Hele-Shaw cell, which he also demonstrates. But you may have come across the effect when pealing up a screen protector or in dealing with a cracked phone screen. In all of these cases, a less viscous fluid — specifically air — is forcing its way into a more viscous fluid, something that it cannot manage without the fluid interface fracturing. (Video and image credit: S. Mould)

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  • Interstellar Jets

    Interstellar Jets

    This JWST image shows a couple of Herbig-Hero objects, seen in infrared. These bright objects form when jets of fast-moving energetic particles are expelled from the poles of a newborn star. Those particles hit pockets of gas and dust, forming glowing, hot shock waves like those seen here in red. The star that birthed the object is out of view to the lower-right. The bright blue light surrounded by red spirals that sits near the tip of the shock waves is actually a distant spiral galaxy that happens to be aligned with our viewpoint. (Image credit: NASA/ESA/CSA/STScI/JWST; via APOD)

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    Kirigami in the Flow

    Kirigami is a paper art that combines folding and cutting to create elaborate shapes. Here, researchers use cuts in thin sheets of plastic and explore how the sheets transform in a flow. Depending on the configuration of cuts, the sheets can stretch dramatically in the flow, creating complex, dynamic, and beautiful wakes. I feel like there must be some applications out there that would benefit from kirigami-induced mixing. (Video and image credit: A. Carleton and Y. Modarres-Sadeghi)

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    Dams Fill Reservoirs With Sediment

    Dams are critical pieces of infrastructure, but, as Grady shows in this Practical Engineering video, they are destined to be temporary. The reason is that they naturally fill with sediment over time. Rivers carry a combination of water and sediment; the latter is critical to healthy shorelines and stable ecology. But while sediment gets carried along by a fast-flowing river, slower flow rates allow sediment to fall out of suspension, as demonstrated in Grady’s tabletop flume. As his river transitions to a deeper, slower-flowing reservoir, sand falls out of the flow, building up colorful strata. The sand and water even create dynamic feedback loops, as seen with the dunes that form in his timelapse and march toward the dam.

    Any long-term plan for a dam has to deal with this inevitable build-up of sediment, and, unfortunately, it’s not a simple or cheap problem to address, as discussed in the video. (Video and image credit: Practical Engineering)

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    On the Mechanics of Wet Sand

    Sand is a critical component of many built environments. As most of us learn (via sand castle), adding just the right amount of water allows sand to be quite strong. But with too little water — or too much — sand is prone to collapse. For those of us outside the construction industry, we’re most likely to run into this problem on the beach while digging holes in the sand. In this Practical Engineering video, Grady explains the forces that stabilize and destabilize piled sand and where the dangers of excavation lie. (Video and image credit: Practical Engineering)

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  • Escape From Yavin 4

    Escape From Yavin 4

    In an ongoing tradition, let’s take another look at some Star Wars-inspired aerodynamics. This year it’s the TIE fighter’s turn. Here, researchers simulate the spacecraft trying to escape Yavin 4’s atmosphere at Mach 1.15. The research poster’s blue contours show pressure contours, with darker colors connoting higher pressures. The bright low pressure region immediately behind the craft suggests a difficult, high-drag ascent and a turbulent, subsonic wake despite the craft’s supersonic velocity. (Image credit: A. Martinez-Sanchez et al.)

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