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Tag: Worthington jet

  • Oil-Slicked Bubble Bursts

    Oil-Slicked Bubble Bursts

    When bubbles at the surface of the ocean pop, they can send up a spray of tiny droplets that carry salt, biomass, microplastics, and other contaminants into the atmosphere. Teratons of such materials enter the atmosphere from the ocean each year. To better understand how contaminants can cross from the ocean to the atmosphere, researchers studied what happens when a oil-coated water bubble pops.

    The team looked at bubbles about 2 millimeters across, coated in varying amounts of oil, and observed their demise via high-speed video. When the bubble pops, capillary waves ripple down into its crater-like cavity and meet at the bottom. That collision creates a rebounding Worthington jet, like the one above, which can eject droplets from its tip.

    The team found that the oil layer’s thickness affected the capillary waves and changed the width of the resulting jet. They were able to build a mathematical model that predicts how wide a jet will be, though a prediction of the jet’s velocity is still a work-in-progress. (Image credit: ะ . ะœะพั€ะพะทะพะฒ; research credit: Z. Yang et al.; via APS)

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

    The Mฤori 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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  • Making a Splash

    Making a Splash

    Since Harold Edgerton’s experiments with stroboscopic photographs in the 1930s, we’ve been fascinated by the shape of splashes. These days students and artists can take advantage of programmable external flashes to capture this split-second moment of impact. Here, a pink-dyed drop of ethanol strikes a jet rising from a pool of glycerin, milk, and food coloring. The resulting splash is umbrella-like, with a thickened rim that shows tiny ligaments of fluid — an early sign of the instability that will ultimately detach droplets from the splash. This image was taken by students in a course that connects art and fluid mechanics. (Image credit: L. Sharpe et al.; via Physics Today)

  • Variations on a Theme by Edgerton

    Variations on a Theme by Edgerton

    In the 1930s, Harold Edgerton used strobed lighting to capture moments too fast for the human eye, including his famous “Milk-Drop Coronet”. Recreating his set-up is far easier today, thanks to technologies like Arduino boards that make timing the drop-strobe-camera sequence simple. This poster is a collage of Edgerton-like images captured by students at Brown University. Even nearly a century after Edgerton, there are countless variations on this beautiful slice of physics: all from the splash of a simple drop striking a pool. (Image credit: R. Zenit et al.)

  • Oil-Covered Bubbles Popping

    Oil-Covered Bubbles Popping

    When bubbles burst, they release smaller droplets from the jet that rebounds upward. Depending on their size, these droplets can fall back down or get lofted upward on air currents that spread them far and wide. Thus, knowing what kind of bubbles produce small, fast droplets is important for understanding air pollution, climate, and even disease transmission.

    The jet from a bubble of clean water.
    The jet from a bubble of clean water is broad and slow, releasing fewer and larger drops.

    In a recent study, researchers compared droplets made by clean, water-only bubbles, and the ones generated from water bubbles with a thin layer of oil coating them. The clean bubbles created jets that were broad and relatively slow moving; this motion produced a few large drops that quickly fell back down.

    The jet from an oil-covered bubble.
    The jet from an oil-covered bubble is skinny and fast-moving. It produces many small droplets.

    In contrast, the oil-slicked bubbles made a narrow, fast-moving jet that broke into many small droplets. These droplets could stay aloft for longer periods, indicating that contaminated water can produce more aerosols than clean. (Image credit: top – J. Graj, bursting – Z. Yang et al.; research credit: Z. Yang et al.; submitted by Jie F.)

  • Beneath the Cavity

    Beneath the Cavity

    When a drop falls into a pool of liquid, it creates a distinctive cavity, followed by a jet. From above the surface, this process is well-studied. But this poster offers us a glimpse of what goes on beneath the surface, using particle image velocimetry. This technique follows the paths of tiny particles in the fluid to reveal how the fluid moves.

    As the cavity grows, fluid is pushed away. But the cavity’s reversal comes with a change in flow direction. The arrows now point toward the shrinking cavity — and they’re much larger, indicating a strong inward flow. It’s this convergence that creates the Worthington jet that rebounds from the surface. And, as the jet falls back, its momentum gets transferred into a vortex ring that drifts downward from the point of impact. (Image credit: R. Sharma et al.)

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    Hollow Drops

    When a partially-air-filled drop hits a surface, it splashes and rebounds in a complex fashion. This video breaks down the physics of the process. Upon impact, a lamella spreads, eventually becoming wavy and unstable along its rim. At the same time, a counterjet forms, growing until it pierces the remaining bubble of the drop. The jet continues to stretch upward due to its momentum, pinching off and forming wobbly satellite drops that finally fall back to the surface. (Image and video credit: D. Naidu and S. Dash)

  • Liquid Sculptures

    Liquid Sculptures

    Snapshots of splashes are nothing new, but few have mastered the art of freezing incredible shapes in water the way Markus Reugels has. His splash photography is mind-boggling, especially knowing that he uses Photoshop only for minor corrections like contrast and removing sensor noise. Fortunately, he’s generous in sharing his expertise. Check out lots more incredible photos and plenty of how-to guides (mostly in German) over at his site. (Image credits: M. Reugels)

  • Liquid Umbrellas

    Liquid Umbrellas

    Two well-timed and properly aligned droplets combine to create these umbrella-like fluid sculptures. The initial drop creates a jet that shoots upward. When the second drop hits that jet, it forms an expanding sheet of liquid like a miniature parasol. The higher the viscosity of the drops, the less lacy and unstable the sheet’s rim will be.

    Although set-ups for these sorts of pictures can be finicky, they’re very doable, even for amateur photographers. In fact, the techniques used here have been around for about a century! (Image and research credit: A. Kiyama et al.)

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    Mud Pots

    Mud pots, or mud volcanoes, form when volcanic gases escape underlying magma and rise through water and earth to form bubbling mud pits. I had the chance to watch some at Yellowstone National Park a few years ago and they are bizarrely fascinating. In this Physics Girl video, Dianna recounts her adventures in trying to locate some mud pots in southern California and explains the geology that enables them there. And if you haven’t seen it yet, check out her related video on the only known moving mud puddle! (Image and video credit: Physics Girl)