FYFD

Category: Phenomena

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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.)

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    The Subtleties of Pipe Flow

    If you put a thumb over your hose’s outlet, you get a faster jet, but how does that affect the flow rate? That’s the question Grady starts from in this Practical Engineering video exploring pipe flow physics. From continuity and control volumes to practical losses, he touches on both the theory and practice behind this all-important aspect of engineering. Pipe flow is often where engineering students begin their studies of fluids, but that doesn’t mean it’s easy! (Video and image credit: Practical Engineering)

  • Microplastics in the Water Column

    Microplastics in the Water Column

    Of the more than 9 billion metric tons of plastic that’s been produced, a mere 9% has been recycled. About 12% has been incinerated, and the remainder is just out there–in our homes, our landfills, and, unfortunately, in our oceans. Exactly where all the plastic is continues to be an active question of research.

    Plastic’s density is similar to that of water; some versions are a little denser than water, and some are a little lighter. So whether a piece of plastic floats at the ocean surface or sinks to the bottom depends on several factors, including its density, size, and shape. A large, dense plastic–think laundry detergent bottles–can float if it displaces enough water; after all, metal ships float!

    But as sunlight and abrasion breaks that big container into smaller fragments, their buoyancy shrinks. Eventually, these small, millimetric pieces sink, carrying our pollution to ecosystems we once thought remote. Some of the highest rates of microplastic ingestion are found in nonmigratory species living between 1200 and 1500 meters below the surface. We may never visit those depths, but our garbage does. (Image credit: iStock/dottedhippo; via Eos)

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    Giant Water Balloon to the Face

    It’s the summertime, so Gav and Dan of the Slow Mo Guys are back to experimenting with giant water balloons. In this video, they send several careening down a slope into Dan’s face. Watching the balloons descend and pop is (unsurprisingly) my favorite part. It’s neat to see how the elasticity of the balloon acts like a beefed-up surface tension to make this enormous blob of water act like an oversized droplet. (Video and image credit: The Slow Mo Guys)

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  • Canyon Swirls

    Canyon Swirls

    For much of the year, Cañon Fiord in the Canadian Arctic lies under ice and snow, but in the summer melt season, colors peek out. Here sea ice and sediment swirl in the fjord in eddies that are kilometers wide. The sediment is largely glacial flour–rock that’s been ground into dust by glaciers. It provides critical nutrients for the marine ecosystem. (Image credit: L. Dauphin; via NASA Earth Observatory)

    Satellite image of sea ice and sediment swirling in Cañon Fiord.