FYFD

Tag: splashing

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    Molten Copper

    In this video, the Slow Mo Guys prove that pouring molten copper in slow motion is every bit as satisfying as one would imagine. Because they pour the metal from fairly high up, they get a nice break-up from a jet into a series of droplets; that’s due to the Plateau-Rayleigh instability, in which surface tension drives the fluid to break up into drops. Upon impact, the copper splashes and splatters very nicely, forming the crown-like splash many are familiar with from famous photos like Doc Edgerton’s milk drop. The key difference between the molten copper and any other liquid’s splash comes from cooling; watch closely and you’ll see some of the copper solidifying along the edges and surface of the fluid as it cools. In this respect, watching the molten copper is more like watching lava flow than seeing water splash. (Video and image credit: The Slow Mo Guys)

  • Crowns On Impact

    Crowns On Impact

    Dropping a partially-filled test tube of water against a table makes the meniscus at the air-water interface invert into a jet of liquid. In some cases, the impact is strong enough to generate splashing crowns of water around the base of the jet. These crowns come in two forms – one with many splashes layered upon one another and the other with only a few splashes and a faster jet. 

    The many-layered splash crowns come from the pressure wave that reflects back and forth from the bottom of the tube to the surface and back. This pressure wave moves at the speed of sound and vibrates the water surface, creating the many splashes. The same reflected pressure wave occurs in the second type of splash crown, but it gets disrupted by cavitation bubbles that form in the water (visible in the lower left image). Instead the splash crowns form from the shock waves generated when the cavitation bubbles collapse. (Image credits: A. Kiyama et al.)

  • Rio 2016: Diving

    Rio 2016: Diving

    Diving is a popular event for spectators, but it can also be rather confusing. We know that divers are rewarded for minimizing their splash, but what exactly does that mean and how do they do it?

    The ideal water entry, called a rip entry by divers, requires a diver to hit the water in a vertical orientation with their arms braced and palms held flat over their head. Striking the water tears open a cavity for the athlete’s body to enter. To minimize splash, the diver wants to fall into this expanding cavity without striking the sides, which would throw up an additional splash. This is the reason for vertical entry. Hand position is also important. If the athlete were to point their fingers, they would create a narrower cavity and larger splash.

    After the athlete enters the water, the cavity closes off under the surface and the water rebounds in a splashy Worthington jet. For the speed and size of human divers, this later splash is essentially unavoidable. What the commentators don’t really tell you, though, is that diving judges are only supposed to judge a diver’s entry up to the point that their feet go under the surface. They’re instructed to ignore everything that happens underwater and after entry. So that big rebound splash we all see isn’t meant to count! (Image credits: A. Pretty/GettyImages; kaorigoto, source)

    Previously: Minimizing splash by being hydrophilic; the physics of skipping rocks and avoiding splashback at the urinal

    Join us throughout the Rio Olympics for more fluid dynamics in sports. If you love FYFD, please help support the site!

  • Crown Splash Sealing

    Crown Splash Sealing

    A sphere falling into water generates a spectacular crown
    splash at the surface. The object’s impact ejects a thin sheet of fluid
    that rises vertically. The air pulled down into the cavity by the
    sphere’s passage makes the air pressure inside the sheet lower than the
    ambient air pressure on the exterior of the sheet. This pressure
    difference is part of what draws the crown inward to seal the cavity. As
    the splash collapses inward and seals, the liquid sheet starts to
    buckle and wrinkle, leaving periodic stripes around the closing neck.
    This so-called buckling instability occurs when the radius of the neck
    collapses faster than the vertical speed of the splash. For more, see
    the research paper or this award-winning video. (Image credit: J. Marston et al., source)

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    Webcast Teaser Reel

    Saturday I topped off a week of water-walking physics by holding a webcast with Professor Tadd Truscott and PhD student Randy Hurd of The Splash Lab. We had an absolutely blast talking about skipping balls, aesthetics and art, sailing, STEM outreach, and much more. The video above is a short teaser for the webcast – you can watch the full hour here. There are demos, a lab tour, and even a chance to learn about how I do FYFD. If you’d like to see or take part in future webcasts, you can do so by becoming an FYFD patron! (Video credit: FYFD)

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    Leaping Mobulas

    Mobula rays engage in some pretty incredible aerial acrobatics. This species of ray, second only to manta rays in size, can jump up to 2 meters into the air. Large groups of mobula rays will engage in this behavior, including both males and females, but it remains unclear to scientists exactly what purpose the jumping serves. It may be a form of communication, which might explain the rays’ apparent preference for belly flopping. By striking the water surface with as much of their body as possible simultaneously, the rays generate both a large splash and a concussive clap that carries through the water. (Video credit: BBC; via J. Hertzberg)

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    Drops on a Porous Surface

    The splashing of a drop upon impact is a remarkably complicated phenomenon. Perhaps surprisingly, the air around the impacting drop plays a major role in determining which drops splash and which don’t. Lowering the air pressure, for example, stops a drop from splashing. The layer of air that gets trapped beneath the spreading edge of a drop during impact seems to be responsible for splashing. As seen in the video above, drops that impact on a leaky surface, where air can escape, do not splash. By varying where leakage is possible on the surface, the researchers can localize where trapping the air matters most. There’s a critical radius during the drop’s spread where, without leakage, air will be trapped and cause the drop to splash. (Video credit: Y. Liu et al.)

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    Granular Jets

    Object impacts in water and other fluids often create cavities that generate jets when they collapse. But impacts on granular materials can produce similar results, forming a cavity, a splash corona, and, under the right circumstances, a jet. This Sixty Symbols video explores the effect of grain size (and thus weight) on the formation of such a rebound jet. Ultimately, the jet behavior is driven by air. When the granular material is poured, air gets trapped between the grains. The impact compresses the grains, forcing the previously trapped air up and out through the cavity created by the impact. Interestingly, once the air pressure is low enough, jet creation is suppressed, not unlike splash suppression in liquids. (Video credit: Sixty Symbols/Univ. of Nottingham)