FYFD

Category: Phenomena

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    Stick Insects in Flight

    There’s something about watching big, awkwardly-shaped insects taking off that doesn’t get old. In this video from Ant Lab, we see giant stick insects spreading their wings and taking off. It’s interesting to note that they seem to be wing-first in their take-off; it doesn’t look like they’re doing much, if anything to propel themselves upward with their legs. Instead, it’s the wings flinging air that gets them up. Check out the flex during the full wingstroke! (Video and image credit: Ant Lab/A. Smith)

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    Rayleigh-Taylor Instability

    When a heavier fluid sits atop a lighter one, the interface between them can be unstable. This means that even a very slight disturbance will be enough to cause fingers of dense (dark) fluid to sink while fingers of the lighter (white) fluid rise. This is known as theย Rayleigh-Taylor instability, and itโ€™s responsible for all kinds of beautiful patterns in our daily lives, like theย mixing of cream in ice coffee. It can causeย cell-like patternsย in acrylic painting,ย umbrella-like forms in ink drops, andย finger-shaped protrusions in a nebula. Itโ€™s an important force inย supernovasย and aย major challenge in achieving fusion.ย 

    The fundamental feature that connects all of these examples is the acceleration of a lighter fluid into a heavier one. For many of them that acceleration is simply the force of gravity, but as with the supernova and nebula, other forces can be responsible for the acceleration. The instability also looks a little different depending on the geometry. The simulation in this post shows a 2D example of the Rayleigh-Taylor instability; three-dimensional versions often look more like umbrellas or mushrooms. (Video and image credit: C. van Heerwaaden)

    Lighter fluid pushes up into a heavier, dark blue fluid.
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    Understanding Hurricane Katrina’s Floods

    Hurricane Katrina’s storm surge flooded roughly 80% of New Orleans when multiple levees breached. In this video, Grady of Practical Engineering breaks down the engineering failures that made Katrina’s flooding so bad. In his typical hands-on fashion, he shows the flaws of the I-wall-topped levee design, and he takes the time to detail how the lessons learned from this disaster propagated into safer engineering practices.

    Plus, he’s got a book coming out next spring. Congrats, Grady! I can’t wait to pick up my copy. (Video and image credit: Practical Engineering)

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  • Gigantic Jet Over the Desert

    Gigantic Jet Over the Desert

    We’re most familiar with the bright, forking lightning bolts that stretch from thunderstorms toward the ground, but there are even more types of lightning. Pictured here is a gigantic jet, a relatively recently-identified atmospheric phenomenon. Gigantic jets occur when a thunderstorm’s electrical charge escapes upward into the ionosphere in less than a second. The red streamers at the top get their color from heating molecular nitrogen. For other unusual types of lightning, check out red sprites and blue jets. (Image credit: M. Vargas; via APOD)

    A gigantic jet rises from a distant thunderstorm into the ionosphere, where is splits into red streamers.
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    Controlling Run-Off With Ponds

    Urban environments are full of impermeable surfaces. Without enough soil for stormwater to soak into, rain turns into run-off, carrying with it all the dirt, oil, and pollutants it picks up. To keep the run-off from turning into a flood, developers often use retention and detention ponds to collect and slowly release stormwater–sometimes with added measures to filter sediment and pollutants first. In this Practical Engineering video, Grady walks us through the logic of these artificial ponds and a few of the many ways they work. (Video and image credit: Practical Engineering)

  • Cometary Knots in the Helix Nebula

    Cometary Knots in the Helix Nebula

    Within the Helix Nebula, a planetary nebula about 650 light-years away, knots of dust and gas stream away from the central star. Though they appear small here, each contains a mass similar to the Earth’s, spread out over an area larger than Pluto’s orbit. Although the structures’ origins are not fully understood, an enduring hypothesis describes them as a Rayleigh-Taylor instability, where the energetic solar wind from the central star blows away denser gas and dust. (Image credit: NASA/ESA/CSA/STScI/JWST/A. Pagan; via APOD)

    Cometary knots in the Helix Nebula, as viewed in infrared light by JWST.
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    How Strings Vibrate

    Many of us have a mental image of strings vibrating like a swinging jump rope, but that’s not quite what you actually see. Instead, plucked strings often look strangely triangular, as Henry explains in this Minute Physics video. This more complicated shape comes from the way the string’s tension responds to the applied force of plucking, striking, or bowing.

    That doesn’t mean that the jump rope picture is entirely wrong, though. The triangular waves seen in the video are the shape you get when all the sine waves of the jump rope model get added together! (Superposition is fun.) (Video and image credit: Minute Physics)

    The triangular wave of a string plucked near one end.
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  • An Iceberg Flips

    An Iceberg Flips

    Footage of a massive iceberg flipping in Greenland has gone viral. The feat took place off the coast of Ilulissat and was caught on a nearby livestream camera. Icebergs shift like this because they melt unevenly, with submerged areas melting faster. As the underwater shape of the iceberg changes, the buoyant forces shift relative to the iceberg’s center of mass, and it flips, eventually settling into a (temporarily) stable orientation. This situation is simpler in the lab version, though; as the video here shows, real icebergs can also rapidly lose mass if they start breaking apart. That, too, can necessitate a flip. (Video and image credit: AfarTV; via Colossal)

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    Levitating By Squeeze Film

    We’ve seen a few different kinds of levitation here over the years, including via acoustic waves, aerodynamics, and Leidenfrost effect. Here, Steve Mould describes something a bit different: a levitation squeeze film driven by ultrasonic transducers. Like a vibrating droplet, the thing keeping surfaces apart here is a thin, lubricating layer of air. The vibration of the ultrasonic transducer squeezes and replenishes the air layer quickly enough that it can keep transducers aloft. Steve even manages to create a miniature airless “air hockey” table with it! (Video and image credit: S. Mould)

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    Blowing Droplets Apart

    In raindrops, ink-jet printing, and spray painting, droplets get broken apart by the air flowing around them. Here, researchers investigate how a jet of fluid can push a droplet from its perch, or–with enough momentum–shatter the droplet. There are some lovely flow visualizations here; it’s especially cool to see the starting vortex ring of the jet push and deform the droplet. (Video and image credit: S. Jain et al.)