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Search results for: “waves”

  • A Drip’s Vortex

    A Drip’s Vortex

    Drip food coloring into water and you can often see a torus-shaped vortex ring after the drop’s impact. That vortex rings form during droplet impact has been well known for over a century, but only recently have we begun to understand the process that leads to that vortex ring. Part of the challenge is that the vortex formation is very small and very fast, but recent work with x-ray imaging has allowed experimentalists to finally capture this event.

    When a drop impacts a pool, surface tension draws some of the pool liquid up the sides of the drop. At the same time, the impact causes ripple-like capillary waves down the sides of the drop. This causes pool liquid to penetrate sharply into the drop, triggering the spirals that mark the forming vortex ring. When drops impact with even higher momentum, multiple vortex spirals can form, as seen on the lower right image. The authors observed as many as four rings during an impact. For more, check out the (open access) article.  (Image and research credit: J. Lee et al., source)

  • Blue Man Group in Slow Mo

    Blue Man Group in Slow Mo

    In their latest video, the Slow Mo Guys team up with the Blue Man Group for some high-speed hijinks, some of which make for great fluidsy visuals. Their first experiment involves dropping a bowling ball on gelatin. The gelatin goes through some massive deformation but comes out remarkably unscathed. Gelatin is what is known as a colloid and essentially consists of water trapped in a matrix of protein molecules. This gives it both solid and liquid-like properties, which means that the energy the bowling ball’s impact imparts can be dissipated through liquid-like waves ricocheting through the gelatin before the elasticity of the protein matrix allows it to reform in its original shape.

    The video ends with buckets of paint flung at Dan. The paints form beautiful splash sheets that expand and thin until surface tension can no longer hold them together. Holes form in the sheet and eat outward until the paint forms thin ligaments and catenaries. As those continue to stretch, surface tension drives the paint to break into droplets, though that break-up may be countered to some extent by any viscoelastic properties of the paint. (Image and video credit: The Slow Mo Guys + Blue Man Group, source)

  • Featured Video Play Icon

    Sky Glow

    This short but spectacular timelapse video shows the Grand Canyon filled with fog. This phenomenon, known as a temperature inversion, occurs when a warm layer of air traps cold, moist air near the ground. As the inversion develops in the video, you can see wisps of clouds popping up in the canyon, seemingly out of nowhere, as moisture evaporated from the surface condenses in the cool air. Once fog fills the canyon, it flows and laps against the canyon’s sides, much like waves on the ocean. In fact, the physics here is quite similar, just at a much slower speed. (Video and image credit: H. Mehmedinovic / SKYGLOWPROJECT; via Gizmodo; submitted by Ian S.)

  • Water Skiing Beetles

    Water Skiing Beetles

    Waterlily beetles employ an unusual method of getting around: they skim across the water surface. The beetles are mostly covered in tiny hairs that help make their body hydrophobic (water-repellent) – a common adaptation for insects that spend their time sitting on the water’s surface – but the beetles also have hydrophilic claws on their legs that help anchor them to the water’s surface. When they need to move quickly, the beetles lean upright and start flapping their wings, creating thrust that helps push them along the interface. Between water’s viscosity and drag from the waves the insect generates, it has to expend a lot of energy for this method of travel – more than these insects do flying in air – but researchers suspect that staying at the surface could remain beneficial for the beetles because it’s easier to locate their floating food sources this way. (Image credit: H. Mukundarajan et al., source; via New Scientist)

  • Breaking Wave

    Breaking Wave

    This animation shows a cinemagraph of a breaking wave photographed by Ray Collins. The motion was inferred and digitally added by a second artist, Jersey Maria. The result is hypnotic, as if we are traveling beside the wave and watching it tear apart ever so slowly. The wave seems to be poised on a tipping point, only breaking up along its back edge, when instinct tells us it will keep steepening and tipping forward until its top curl crashes down in a wave of white foam. Surf photography like Collins’ work shows us an alternative perspective on waves, their power frozen into a single instant. Reanimated, it feels like we’re seeing the wave in hyper-slow-motion, watching every tiny movement of water before everything crashes down. Even if it’s not physically realistic, it is an awesome view.  (Image credit: R. Collins / J. Maria, source, original; via Iwan A.)

  • Acrylic and Oil

    Acrylic and Oil

    Photographer Alberto Seveso is well-known for ink in water art, some of which FYFD has featured previously (1, 2, 3). More recently, he’s been experimenting with alternative methods, dropping fluids like acrylic paint into sunflower oil. The effect is quite different but no less beautiful. Because the paint and oil are immiscible, the boundaries between the two fluids are much more clearly defined and highlighted in an iridescent sheen. Instead of appearing like billowing waves of silk, the paint forms abstract and alien shapes driven by gravity, inertia, and density differences. For many more great examples, check out Seveso’s website. (Photo credit: A. Seveso)

  • The Kamifusen

    The Kamifusen

    The kamifusen is a traditional Japanese toy made of colorful paper. It resembles a beach ball, but unlike that toy, the kamifusen has an open hole at one end. Given that hole, one might expect the toy to deflate when struck, but the opposite is true – a deflated kamifusen inflates itself when bounced. The key to this counter-intuitive behavior comes from a combination of fluid dynamics and solid mechanics.

    When the kamifusen bounces off a player’s hand, it is compressed, which increases pressure inside the toy and forces some air out. Elastic waves rebound through the ball’s paper walls, much like seismic waves traveling outward from an earthquake. Those waves re-expand the toy’s walls, dropping the interior pressure and pulling air in from the outside. Although the pressure spike from impact is larger, its duration is short compared to the low pressure generated by the subsequent elastic waves. As a result, more air flows into the toy than is knocked out, and so the kamifusen inflates. For more, check out this explanation at Physics Today.  (Image and research credit: I. Fukumori, source; submitted by E. van Andel)

  • Bottle Rocket Shock Diamonds

    Bottle Rocket Shock Diamonds

    Mach diamonds or shock diamonds can often be seen in the exhaust of rocket engines. Here they’re shown in high-speed video of a bottle rocket’s launch. The rocket’s exhaust exits at a pressure that is higher than the surrounding atmosphere, which causes the exhaust to bulge outward and forms two expansion fans, seen in pink, to lower the pressure. The pressure actually drops too low, however, causing shock waves, seen in turquoise, to form in order to raise the exhaust’s pressure. This back-and-forth between shock waves and expansion fans continues, forming the diamond shapes we see. Each subsequent set gets weaker as the exhaust closes in on the right pressure, and ultimately the series of diamonds fades into turbulence. (Image credit: P. Peterson and P. Taylor, source)

  • Shocks on a Wing

    Shocks on a Wing

    Commercial airliners fly in what is known as the transonic regime at Mach numbers between 0.8 and 1.0. While the airplane itself never exceeds the speed of sound, that doesn’t mean that there aren’t localized regions where air flows over the airplane at speeds above Mach 1. In fact, it’s actually possible sometimes to see shock waves on the top of airliner’s wings with nothing more than your eyes. The animations above show shock waves sitting about 50-60% of the way down the wing’s chord on a Boeing 737 (top) and Airbus A-320 (bottom). The shock wave looks like an unsteady visual aberration sitting a little ways forward of the wing’s control surfaces.

    The wings themselves are shaped so that these little shock waves are relatively stationary and remain upstream of the flaps pilots use for control. Otherwise, the sharp pressure change across a shock wave sitting over a control surface could make moving that surface difficult. This was one of the challenges pilots first trying to break the sound barrier faced. (Image credits: R. Corman, source; agermannamedhans, source)

  • Breaking the Wave Speed Limit

    Breaking the Wave Speed Limit

    Whirligig beetles are small surface swimming insects. As they race across the water surface, they create both visible and unnoticeable waves on the water. These waves are the result of both surface tension and gravity. Typically, it’s the wavelength of the gravity waves that limit a swimmer or boat’s speed. When the wavelength of the gravity waves a swimmer creates meets the size of the swimmer, the waves generated ahead of the swimmer start to reinforce the waves forming at the back of the swimmer. This traps the swimmer (or boat) in a trough between its bow and stern waves and limits the max speed of the swimmer since overcoming this critical hull speed requires excessive amounts of power.

    The tiny whirligig beetle overcomes this natural speed limit cleverly. It is smaller than the shortest possible gravity wave in water. Thus, it can never be trapped between its bow and stern waves! This allows the tiny swimmer to zip across the water’s surface at speeds above 0.5 m/s. That’s over 30 beetle body lengths per second! (Image credit: H. L. Drake, source; research credit: V. Tucker; submitted by Marc A.)

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