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Search results for: “waves”

  • Skipping Squishy Spheres

    Skipping Squishy Spheres

    Skipping a stone on water requires a flat, disk-like stone thrown at a shallow angle, but elastic spheres are remarkable skippers, too, even at higher impact angles. Researchers at the Splash Lab have just published their work on why these balls skip so well. As seen in the top animation, the elastic spheres deform on impact, flattening to a more disk-like shape that rides at an angle of attack relative to the air-water interface. Both features are important to the spheres’ enhanced skipping. By flattening, the sphere comes into greater contact with the water and by orienting at a larger angle of attack, the sphere increases the vertical component of force the water generates on the sphere. It’s this vertical force that lifts the sphere up and lets it keep bouncing.

    Because the ball is soft, it keeps deforming after its impact and bounce (see top animation). For some skips, the timescale of the sphere’s elastic waves is smaller than the length of time the sphere is in contact with the water. When this is the case, the sphere’s elastic waves will affect the impact cavity in the water, forming what the researchers call a

    matryoshka cavity, after the Russian nesting dolls. An example is shown in the second animation. For more, check out the USU press release, the original paper, or the award-winning video they made a few years ago.  (Image credits: J. Belden et al./The Splash Lab)

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    Wave Clouds

    In this video, Sixty Symbols tackles the physics of wave clouds. When air flows over an obstacle like a mountain, the air can begin to oscillate downstream, forming what is known as a lee wave. As the air bobs up and down, it will cool or warm according to its altitude. At cooler conditions, if the air is moist, it can condense into a cloud at the peak of its oscillation. If you observe this behavior over time, you get what appear to be regularly-spaced stripes of clouds. This is actually a pretty common phenomenon to see, depending on where you live. It’s an example of internal waves in the atmosphere.  (Video credit: Sixty Symbols)

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  • Fluids Round-Up

    Fluids Round-Up

    New year, new (or renewed) experiments. This is the fluids round-up, where I collect cool fluids-related links, articles, etc. that deserve a look. Without further ado:

    (Video credit and submission: Julia Set Collection/S. Bocci; image credit: IRPI LLC, source)

  • Beach Cusps

    Beach Cusps

    This composite photo shows the arc of the sun over Lulworth Cove in England during the December solstice. The low sun angle reveals a distinctive circular diffraction pattern of waves inside the cove. Along the shoreline, the beach has eroded into a regular, arc-like pattern known as beach cusps. Although there are multiple theories about how cusps form, their pattern is self-sustaining. They consist of a horn of coarse materials that projects into the water and an arc of finer sediments called an embayment. When incoming waves hit the horn, they slow down, depositing heavier coarse sediment on the horn while lighter, fine particles are carried further ashore. (Image credit: C. Kotsiopoulos; via APOD; submitted by jshoer)

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    Inside a Popping Bubble

    Popping a soap bubble is more complicated than what the eye can see. In high-speed video, we find that the action is very directional, with the soap bubble film pulling away from the point of rupture. As it does so, waves, like those in a flapping flag, appear along the surface and strings of fluid form along the edge of the film before breaking into droplets. This video takes matters a step further, looking at what happens to air inside a bubble when it pops. Those subtle waves and strings of fluid we see in the high-speed rupture have a distinctive effect on air inside the bubble. As the film pulls away, it leaves behind a rippled, wavy surface rather than a smooth sphere of foggy air. (Video credit: Z. Pan et al.)

  • Jovian Belts and Zones

    Jovian Belts and Zones

    Jupiter’s colorful cloud bands alternate between dark belts and light zones. The bands mark convection cells in Jupiter’s atmosphere, and, like on Earth, powerful jet streams form due to this atmospheric heating and the planet’s rotation. The jet winds can even move in opposite directions, creating strong shear forces between neighboring cloud bands. The shear helps drive Kelvin-Helmholtz instabilities in the clouds, resulting in the regularly spaced waves and vortices seen along the edges of some bands. (Image credit: NASA/ESA; via APOD)

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    Early Rocket Launch

    Pre-dawn launches provide some of the most dramatic rocket footage. This video is from an October 2nd Atlas V launch, and the really fun stuff starts at about 0:34. As the rocket climbs to higher altitudes, the atmospheric pressure around it decreases. As a result of this low pressure, the rocket’s exhaust gases balloon outward in a giant plume many times larger than the rocket. This happens in every launch, but it’s visible here because the rocket is at such a high altitude that its exhaust is being lit by sunlight while the observers on the ground are still in the dark. The ice crystals in the exhaust–much of the rocket’s exhaust is water vapor–reflect sunlight down to the earth. Around 0:47, a cascade of shock waves ripples through the plume just before the first-stage’s main engine cuts off. Once the engine stops firing, there’s no more exhaust and the plume ends. (Video credit: Tampa Bay Fox 13 News; submitted by Kyle C)

  • Shock Diamonds

    Shock Diamonds

    Rocket engine exhaust often contains a distinctive pattern known as shock diamonds or Mach diamonds. These are a series of shock waves and expansion fans that increase and decrease, respectively, the supersonic exhaust gases’ pressure until it equalizes with atmospheric pressure. The bright glowing spots visible to the naked eye are caused by excess fuel in the exhaust igniting. As awesome as shock diamonds look, they’re actually an indication of inefficiencies in the rocket: first, because the exhaust is over- or underexpanded, and second, because combustion inside the engine is incomplete. Both factors reduce a rocket engine’s efficiency (and both are, to some extent, inescapable). (Photo credit: XCOR)

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    Bubbles and Hurricanes

    You may think of soap bubbles as a childhood plaything, but there’s a lot to be learned from them. In her newest video, Dianna of Physics Girl explores some of the fascinating research scientists use soap bubbles for and how you can recreate some of their experiments at home. Scientists have used bubbles to explore how atmospheric vortices behave, how to tie knots in fluids, how grass waves in the wind, and even how explosive detonations occur. Just modeling bubbles and foams can be incredibly complex. It turns out the humble bubble has quite a lot to teach us. (Video credit: Physics Girl/PBS Digital Studios)

  • Wave Clouds Over the Galapagos

    Wave Clouds Over the Galapagos

    This dramatic example of Kelvin-Helmholtz clouds was taken near the Galapagos Islands last week. The shark-fin-like clouds are the result of two air layers moving past one another. The velocity difference at their interface creates an unstable shear layer that quickly breaks down. The resemblance of the clouds to breaking ocean waves is no coincidence – the wind moving over the ocean’s surface generates waves via the same Kelvin-Helmholtz instability. In the case of the clouds above, the lower layer of air was moist enough to condense, which is why the pattern is visible. Clouds like these don’t tend to last for long because the disturbances that drive the instability grow exponentially quickly, leading to turbulence. (Image credit: C. Miller; via Washington Post; submitted by @jmlinhart)

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