FYFD

Tag: standing waves

  • Lenticular Landscape

    Lenticular Landscape

    Mountain ridgelines push oncoming winds up and over their peaks, creating the conditions for some spectacular condensation. If the displaced air is moist enough, it cools and condenses into a cloud that appears to hover over the peak. In reality, winds are constantly moving up and over the mountain, condensing into visible cloud where the temperature is cool enough and then morphing back to water vapor once temperatures increase. This process can create stacked lenticular clouds like those seen here. This spot in New Zealand sees lenticular clouds so often that the formation has its own name: Taieri Pet! (Image credit: satellite image – L. Dauphin, b/w – National Library; via NASA Earth Observatory)

    Black-and-white photo of an instance of the Taieri Pet lenticular cloud structure.
    Black-and-white photo of an instance of the Taieri Pet lenticular cloud structure.
  • A Game of Toss

    A Game of Toss

    Over the past few years, we’ve seen lots of droplets bouncing and walking on waves. But today’s example is a little different. In this set-up, the wave is a large standing wave that sloshes from side-to-side in a narrow container. As it does, the wave catches and tosses a large ~3mm water droplet. The system is surprisingly stable, with this game of catch lasting for tens of thousands of cycles and up to 90 minutes before the droplet coalesces. The researchers found that, if the droplet tries to wander from its spot, the oscillating surface wave corrects it, guiding the droplet back to the optimal position. (Image and research credit: C. Sandivari et al.; via APS Physics; submitted by Kam-Yung Soh)

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    Pumping With Faraday Waves

    Vibrate a liquid pool vertically, and it will form a pattern of standing waves known as Faraday waves. Here, researchers confine those waves to a narrow ring similar in size to the wave. The confinement causes a type of secondary flow — a streaming flow — beneath the water surface. As a result, the wave pattern rotates around the ring. The applications of this rotation are pretty neat. As the team demonstrates, it can drive complex fluid networks and even create a pump! (Image and video credit: J. Guan et al.)

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    Leaky Resonance

    Some resonators aren’t perfect — nor are they meant to be! Here, researchers experiment with resonance using a disk shaking up and down over a pool of water. The disk never touches the water, but its movement makes the air above the water move in and out, like a miniature, changeable wind. The air flow distorts the water surface, creating waves just tens of microns high. Beneath the disk, the water forms standing waves, indicating resonance.

    But the waves don’t stay under the disk. Beyond its edge, we see traveling waves moving outward, carrying some of the disk’s energy with them. This leakage is actually how many musical instruments, like a guitar, work. When the guitar strings are plucked, their vibrations are transmitted into the body of the guitar through its bridge, where the strings are anchored. The body acts as a resonator, amplifying the sound, some of which leaks out the sound hole. (Image and video credit: U. Jain et al.)

  • Diamond-Shaped Waves

    Diamond-Shaped Waves

    Strong winds blowing across Lake Michigan created this diamond-shaped wave pattern after the incoming waves reflected off the breakwater on the right. The formal name for these waves are clapotis gaufré, meaning “waffled standing waves”. As seen in the animation above, the waves aren’t perfect standing waves; otherwise they would stay in one place rather than propagating toward shore. This happens because the angle of reflection is not exactly 90 degrees.

    As neat as clapotis gaufré waves look, they’re a significant problem for the builders of coastal infrastructure. The waves generate vortices underwater that are extremely good at eroding underlying sediment. (Image and video credit: T. Wenzel; via EPOD; submitted by Vince D.)

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    Psychedelic Faraday Waves

    Vibrate a pool of water and above a critical frequency, a pattern of standing waves will form on the surface. These are known as Faraday waves after Michael Faraday, who studied the phenomenon in the early half of the nineteenth century. The kaleidoscopic view of them you see here comes from photographer Linden Gledhill, who used a high-speed camera and an LED ring light reflecting off the water to capture the changing motions of the waves. The wave patterns oscillate at half the frequency of the driving vibration, and, as the driving frequency changes, the wave patterns shift dramatically. Higher frequencies create more complicated patterns. (Image and video credit: L. Gledhill)

  • Visualizing Acoustic Levitation

    Visualizing Acoustic Levitation

    The schlieren photographic technique is often used to visualize shock waves and other strong but invisible flows. But a sensitive set-up can show much weaker changes in density and pressure. Here, schlieren is used to show the standing sound wave used in ultrasonic levitation. By placing the glass plate at precisely the right distance relative to a speaker, you can reflect the sound wave back on itself in a standing wave, seen here as light and dark bands. The light bands mark the high-pressure nodes, where the pressure generated by the sound waves is large enough to counteract the force of gravity on small styrofoam balls. This allows them to levitate but only in the thin bands seen in the schlieren. Move the plate and the standing wave will be disrupted, causing the bands to fade out and the balls to fall. (Video and image credit: Harvard Natural Sciences Lecture Demonstrations)

  • Lenticular Clouds

    Lenticular Clouds

    Lenticular clouds are peculiar enough that, for years, they’ve been mistaken for other things – often UFOs. These lens-shaped clouds tend to form near mountainous terrain, where air gets forced up and over the topology. If there’s a drop in temperature as the air rises, water can condense out to form the cloud. Once the air sinks, it warms enough that condensation is no longer possible. The result is a cloud that appears to stand still even though the air is moving. In reality, the cloud is constantly reforming from the moisture of incoming air. Lenticular clouds can form as a single layer, or they can form stacks like the one pictured above in Boulder, Colorado. They may seem odd, but they’re actually fairly common. If you live near hills or mountains, keep an eye out for them!  (Image credit: @bayouowl; via Ilya L.)

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    Songs in Soap

    There are many beautiful ways to visualize sound and music – Chris Stanford’s fantastic “Cymatics” music video comes to mind – but this is one I haven’t seen. This visualization uses a soap film on the end of an open tube with music playing from the other end. You can see the set-up here. The result is a fascinating interplay of acoustics, fluid dynamics, and optics. As sound travels through the tube, certain frequencies resonant, vibrating the soap film with a standing wave pattern (3:20). At the same time, interference between light waves reflecting off the front and back of the soap film create vibrant colors that show the film’s thickness and flow.

    When the frequency and amplitude are just right, the sound excites counter-rotating vortex pairs in the film (0:05), mixing areas of different thicknesses. With just a single note, the vortex pairs appear and disappear, but with the music, their disappearance comes from the changing tones. Watching the patterns shift as the film drains and the black areas grow is pretty fascinating, but one of the coolest behaviors is how the acoustic interactions are actually able to replenish the draining film (2:15). Because the tube was dipped in soap solution, some fluid is still inside the tube, lining the walls. With the right acoustic forcing, that fresh fluid actually gets driven into the soap film, thickening it.

    There are several more videos with different songs here – “Carmen Bizet” is particularly neat – as well as a short article summarizing the relevant physics for those who are interested. (Video and research credit: C. Gaulon et al.; more videos here)

  • Psychedelic Cymatics

    Psychedelic Cymatics

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    Cymatics are the visualization of vibration and sound. Here photographer Linden Gledhill has taken a simple speaker vibrating a dish of water and turned it into some incredible art. When you vibrate liquids like water up and down, it disturbs the usually flat air-water interface and creates waves on the surface. These Faraday waves are a standing wave pattern that differs depending on which sound is being played. By combining the wave patterns with LED lighting and strobe effects, Gledhill creates some remarkable images that combine sound, light, and fluid dynamics all in one. If you watch the video (make sure to hit the HD button!), you’ll see the patterns in motion and hear the sounds used to generate them. In the last clip (around 0:19), he’s added glitter to the set-up, which highlights the circulation within the vibrating fluid. As you can see, there are strong recirculating regions in each lobe of the pattern, but other areas, like the center region are almost entirely stationary. You can see more photos from the project in his Flickr feed. Special thanks to Linden for letting me post the video of his work, too! (Video and image cred

    its and submission: L. Gledhill)

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