The shock waves propagating in front of an Atlas V rocket after launch decimate a rainbow-like effect called a sun dog. #
Search results for: “shock wave”
Tongan Eruption
In January 2022, the Hunga Tonga-Hunga Ha’apai volcano erupted spectacularly, sending waves around the world through the air, water, and ground. In many ways, it was unlike any eruption scientists have observed, though they think it bears similarities to the 1883 eruption at Krakatoa. This video summarizes some of the research to come out of the eruption, looking at how waves propagated, what aerosols the volcano pushed high into the atmosphere, and what the long-term effects of the eruption may be. (Video credit: Science)
Landslide-Triggered Tsunamis
After the 2018 Anak Krakatoa eruption, a tsunami that ricocheted through the surrounding waters, killing hundreds on nearby islands. The source of that tsunami was a small landslide. Once the air cleared and researchers could assess how much material slid into the ocean, they were shocked that such a small volume created so much destruction.
Now new efforts are revealing the linkage between landslides and the waves they make. Researchers released glass beads into a tank of water, observing the waves that form as the beads run out. Depending on the relative initial height of the beads compared to the water depth, they observed three different kinds of waves. Not only that, they were able to connect the granular mechanics of the landslide to the hydrodynamic formation of waves, allowing predictions of the waves that will form for a given landslide.
Currently, the predictive model isn’t sophisticated enough to handle a geometry as complex as that of the Anak Krakatoa landslide, but it’s an important step toward understanding — and potentially mitigating the damage of — future oceanside landslides. (Image and research credit: W. Sarlin et al.; via APS Physics; submitted by Kam-Yung Soh)
Turbulence and Star Formation
Space, as I’ve discussed previously, is surprisingly full of matter, especially clouds of dust. And yet the rate of star formation we observe is bizarrely low; the Milky Way, for example, produces only about one solar mass worth of new stars every year. If gravity were the sole force driving star formation, we’d see far more stars forming. Recent research suggests that turbulence plays a major role in regulating the star formation process, both by countering gravity’s attempts to collapse gases into a proto-star and by creating supersonic shocks that drive material together to jump-start star formation. There seem to be other important ingredients as well: young stars tend to form jets that blow material back into the interstellar clouds they’re forming in, feeding the turbulent background. For more, check out Physics Today. (Image credit: ESA/NASA/Hubble/ESO, via APOD; research credit: C. Federrath)
Seeing the Wake
Hot exhaust gases churn in the wake of this climbing B-1B Lancer. The high temperature of the exhaust changes the density and, thus, the refractive index of the gases relative to the atmosphere. Light traveling through the exhaust gets distorted, making the highly turbulent flow visible to the human eye. Note how the four individual engine exhaust plumes quickly combine into one indistinguishable wake. This is typical for turbulence; it’s hard to track where any given fluctuations originally came from. The airplane’s wingtip vortices are just visible as well, if you look closely. (Image credit: T. Rogoway; submitted by Mark S.)
Tendrils of Fog
Fog snakes its way from the ocean into the Strait of Juan de Fuca in this animation constructed from satellite imagery. The strait lies between Vancouver Island and the Olympic Peninsula in the Pacific Northwest. Fogs like this form when skies are clearer and heat from the surface is able to escape upward. The surface air then cools and condenses into fog. Steady winds pushed fog into the strait over the course of about 9 hours. There’s a remarkable level of detail in the satellite images, taken by the new GOES-16 satellite that launched in late 2016. Notice the ragged wave front as the fog stretches eastward and the shock-wave-like lines behind it in the strait. Both result from interactions between the fog cloud and the shape of the land masses it’s encountered. (Image credit: NASA Earth Observatory)
Underwater Explosions in Slow Mo
The Slow Mo Guys bring their high-speed skills to underwater explosions in this new video. The physics of such explosions is very neat (but also incredibly destructive). When the fuse ignites, a blast wave travels outward in a sphere, creating a bubble filled with gas. Eventually, the pressure of the surrounding water is too great for the bubble to expand against. When its expansion slows, that much larger pressure from the surrounding water starts to crush the bubble back down. Decreasing the volume of the bubble raises its pressure and its temperature again, and this often reignites any leftover fuel and oxidizer left in the bubble. The secondary shock bubble will re-expand, kicking off another round of expansion and collapse. (Video credit: The Slow Mo Guys; submitted by potato-with-a-moustache)
What Sound Looks Like
NPR’s Skunk Bear Tumblr has a great new video on the schlieren visualization technique. The schlieren optical set-up is relatively simple but very powerful, as shown in the video. The technique is sensitive to variations in the refractive index of air; this bends light passing through the test area so that changes in fluid density appear as light and dark regions in the final image. Since air’s density changes with temperature and with compressibility, the technique gets used extensively to visualize buoyancy-driven flows and supersonic flows. Since sound waves are compression waves which change the air’s density as they travel, schlieren can capture them, too. (Video credit: A. Cole/NPR’s Skunk Bear)
Aurora From Space
An aurora, as seen from the International Space Station, glows in green and red waves over the polar regions of Earth. These lights are the result of interactions between the solar wind–a stream of hot, rarefied plasma from the sun–and our planet’s magnetic field. A bow shock forms where they meet, about 12,000-15,000 km from Earth. The planet’s magnetic field deflects much of the solar wind, but some plasma gets drawn in along field lines near the poles. When these energetic particles interact with nitrogen and oxygen atoms in the upper atmosphere, it can excite the atoms and generate photon emissions, creating the distinctive glow. Similar auroras have been observed on several other planets and moons in our solar system. (Photo credit: NASA)
Rocket Sonic Boom
Originally posted: 22 July 2010 This video of the NASA Solar Dynamics Observatory’s launch is such a favorite of mine that it was part of the original inspiration for FYFD and was the very first video I posted. Watch closely as the Atlas V rocket climbs. At 1:51 you’ll see a rainbow-like cloud in upper right corner of the screen. This effect is created by sunlight shining through ice crystals of the cloud. A couple seconds later you see pressure waves from the rocket propagate outward and destroy the rainbow effect by re-aligning the ice crystals. Just after that comes the announcement that the vehicle has gone supersonic. The atmospheric conditions of the launch happened to be just right to make those pressure waves coming off the rocket visible just before they coalesced into a leading shockwave. (Video credit: B. Tomlinson)
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