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Search results for: “waves”

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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)

  • Flying Fragments

    Flying Fragments

    Flying fragments can be a big danger in explosions. Shown above are two shadowgraph images of 1 gram explosives originally packed in solid containers. Each explosion produced a visible spherical shock wave, about 1 meter across in both pictures. On the left side, the container has fragmented into large pieces, each of which travels near to but less than the speed of sound. On the right, the fragments are much smaller, but many of them are traveling at supersonic speeds ahead of the main shock wave. If you look closely, you can even see faint Mach cones extending from each fragment. In a real, full-scale explosion, these shards would strike like a hail of bullets ahead of the blast wave. (Image credit: G. Settles)

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    The Mantis Shrimp’s Left Hook

    The mantis shrimp is a tiny, clown-colored juggernaut of underwater physics. Some species have modified claws that serve as clubs for punching their prey, and the mantis shrimp swings that club fast – its acceleration is comparable to a bullet’s! Moving that quickly in water causes a drastic drop in local pressure, low enough to form a cavitation bubble. Such low-pressure bubbles themselves are not particularly dangerous, but their collapse is incredibly violent, especially near a solid surface, like the shell of the shrimp’s prey. Collapsing cavitation bubbles can send out shock waves, shatter glass, and even generate light. In the case of the mantis shrimp, it’s more than enough to stun, if not outright kill, its prey. (Video credit: Physics Girl)

  • Vortex Reconnection

    Vortex Reconnection

    In slow motion, vortex rings can be truly stunning. This video shows two bubble rings underwater as they interact with one another. Upon approach, the two low-pressure vortex cores link up in what’s known as vortex reconnection. Note how the vortex rings split and reconnect in two places – not one. According to Helmholtz’s second theorem a vortex cannot end in a fluid–it must form a closed path (or end at a boundary); that’s why both sides come apart and together this way. After reconnection, waves ripple back and forth along the distorted vortex ring; these are known as Kelvin waves. Some of those perturbations bring two sides of the enlarged vortex ring too close to one another, causing a second vortex reconnection, which pinches off a smaller vortex ring. (Image source: A. Lawrence; submitted by Kam-Yung Soh)

    Note: As with many viral images, locating a true source for this video is difficult. So far the closest to an original source I’ve found is the Instagram post linked above. If you know the original source, please let me know so that I can update the credit accordingly. Thanks!

  • Impressionist Gibraltar

    Impressionist Gibraltar

    Swirls of phytoplankton make this satellite image of Gibraltar look like an Impressionist painting. The photo is a composite of data from several instruments, with colors enhanced to highlight features of the phytoplankton blooms. The tiny plankton act as tracer particles that reveal some of the complex flow between the North Atlantic and the Mediterranean. Although narrow, the Strait at Gibraltar has deep and complex terrain that was formed during a breach flood event millions of years ago. Water flowing through that terrain sets up enormous and complicated waves well beneath the ocean surface. These drive some of the turbulence that we see here as the blue swirls east of the Strait. (Image credit: NASA/N. Kurig; via NASA Earth Observatory)

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    Kelvin-Helmholtz Instability

    Sixty Symbols has a great new video explaining the laboratory set-up for demoing a Kelvin-Helmholtz instability. You can see a close-up from the demo above. Here the pink liquid is fresh water and the blue is slightly denser salt water. When the tank holding them is tipped, the lighter fresh water flows upward while the salt water flows down. This creates a big velocity gradient and lots of shear at the interface between them. The situation is unstable, meaning that any slight waviness that forms between the two layers will grow (exponentially, in this case). Note that for several long seconds, it seems like nothing is happening. That’s when any perturbations in the system are too small for us to see. But because the instability causes those perturbations to grow at an exponential rate, we see the interface go from a slight waviness to a complete mess in only a couple of seconds. The Kelvin-Helmholtz instability is incredibly common in nature, appearing in clouds, ocean waves, other planets’ atmospheres, and even in galaxy clusters! (Image and video credit: Sixty Symbols)

  • Break-Up of the Chelyabinsk Meteor

    Break-Up of the Chelyabinsk Meteor

    In 2013, a meteor about 20-meters in diameter broke up over Chelyabinsk, Russia in a dramatic display that damaged buildings within 100 km and injured more than 1200 people. To better understand the threat presented by such objects, NASA has been conducting 3D, hypersonic simulations like the one shown here. The meteor material is shown in gray and black. Brighter colors like red and yellow indicate the hot, high-pressure shock wave caused when the meteor slams into the atmosphere. Aerodynamic effects quickly erode the meteor, ripping it into pieces that disperse energy explosively in the atmosphere. While you might think the meteor breaking up is good for us, it’s actually the blast waves from its break-up that cause the most damage.  (Image and video credit: NASA, source; via Gizmodo)

  • Cavitating

    Cavitating

    Cavitation happens when the local pressure in a liquid drops below its vapor pressure. A low-pressure bubble forms, typically very briefly, when this occurs. These bubbles are spherical unless they form near a surface. In that case, the bubbles take on a flatter, oblong shape. As they collapse, the bubbles form a jet, like the one seen inside the bubble above. The jet extends through the bubble and stretches into a funnel shaped protrusion on the bubble’s far side. Eventually, the whole shape becomes unstable and breaks into many smaller bubbles. Shock waves can be generated in the collapse, too; often the jet generates at least two in addition to the ones created when the bubble reaches its minimum size. This is part of why cavitation can be so destructive near a surface. (Image credit: L. Crum)

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    Shadows of Flow

    In the latest Veritasium video, Derek demonstrates how to see gas motions that are normally invisible using a schlieren photography set-up. Schlieren techniques have been important in fluid dynamics for well over a century, and Derek’s set-up is one of the two most common ways to set up the technique. (The other method uses two collimating mirrors instead of a single spherical or parabolic one.) As explained in the video, the schlieren optical set-up is sensitive to small changes in the refractive index, making density changes or differences in a gas visible. This makes it possible to distinguish gases of different temperatures or compositions and even lets you see shock waves in supersonic flows. (Video and image credit: Veritasium; submitted by Paul)

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    Asperitas Sunset

    Asperitas clouds, previously known as undulatus asperatus, are the most recently recognized cloud type. These clouds make the sky look like the ocean rolling in waves. Photographer Mike Olbinski, on a recent storm chase earlier this month, caught these spectacular asperitas clouds near sunset. The clouds’ effect is unusual under normal circumstances and completely surreal with this lighting. Check out the video for the full effect. Olbinski caught the clouds on the outskirts of a dying storm cell. That’s a common place to see these formations; despite their ominous appearance, they do not develop storms and are more often seen as storms are ending. (Video and image credit: M. Olbinski; h/t to Paul vdB)

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