FYFD

Tag: physics

  • Spinning Tops

    Spinning Tops

    What does the flow look like around a spinning top? Here, researchers used dye to visualize what happens in a Newtonian fluid (like air or water) as well as a viscoelastic fluid. The Newtonian fluid (upper images) divides into two circulating zones, one below the top and one above. They both take the shape of a toroidal, or donut-shaped, vortex, visible here in cross-section.

    The long molecules of the viscoelastic fluid lend it elasticity to resist stretching. The result is a very different flow field. Beneath the top, there’s still a toroidal vortex, though it appears tighter. But around the upper part of the top, there’s a butterfly-like region of recirculation! (Image credit: B. Keshavarz and M. Geri)

  • Superhydrophobic Drag

    Superhydrophobic Drag

    Using air or bubbles to reduce drag on boats is a popular idea, whether using supercavitation, the Leidenfrost effect, or superhydrophobic coatings. But most of the experiments done thus far use spheres rather than realisitic boat shapes. In this study, the researchers used two model boats — one with a hydrofoil and the other in a conventional motorboat shape — and applied superhydrophobic coatings to different parts of the model to see how superhydrophobicity affected the overall drag.

    Perhaps surprisingly, they found that superhydrophobic coatings can actually increase the drag! The effect was particularly stark for the hydrofoil boat (Image 2), where the surface jets (lower half) caused by the superhydrophobic coating slowed the boat by 30% compared to its unmodified speed (upper half).

    For the speedboat, a superhydrophobic hull made no overall difference in its drag, though it changed how water splashed in its wake. And coating the boat’s propeller was particularly detrimental, resulting in a speed up to three times slower. Overall, the study suggests that superhydrophobic coatings may be useful in some circumstances, but they have to be applied carefully, as they can have negative impacts, too. (Image credits: top – S. Anghan, others and research credit: I. Vakarelski et al.)

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    Fagradalsfjall Volcano

    We’ve seen a lot of drone photography from volcanic eruptions in the last few years, but this footage from Iceland Aerials seems even more daredevil than usual. In this video, you can cruise over fountains of lava and watch as it cascades downhill. The perspective on some of these shots is absolutely unreal; it almost seems like it would have to be CGI. (Video credit: Iceland Aerials; via Colossal)

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    Eruption in a Box

    In layers of viscous fluids, lighter and less viscous fluids can displace heavier, more viscous liquids. Here, researchers demonstrate this using four fluids sandwiched between layers of glass and mounted in a rotating frame. (Think of those liquid-air-sand art frames found in museums but bigger!)

    In their first example, each layer of fluid is denser than the one beneath it, so buoyancy forces the lowest layer — air — to rise. The air pushes its way through the more viscous layer of olive oil, then slowly makes its way through the even more viscous glycerin before bursting through the last layer in an eruption. As the team varies the viscosity and miscibility of the layers, the movement of the buoyant fluids through the viscous layers changes dramatically. (Image and video credit: A. Albrahim et. al.)

  • Bendable Ice

    Bendable Ice

    Ice — as we typically encounter it — is extremely brittle and easily broken. That’s due to defects in the ice, places where atoms have settled into a spot that does not match the perfect crystalline alignment. Because tiny defect-free threads of ice made by researchers turn out to be wildly flexible!

    To make these perfect ice strands, each of which is a tiny fraction of the thickness of a human hair, researchers applied an electric voltage to a needle in a water-vapor-filled chamber. The technique condensed ice microfibers with perfect crystal structures in a matter of seconds. When bent, the microfibers actually shift from one crystalline arrangement to another in order to carry stress, and once the force is removed, the thread reverts back to its initial straight form. (Image and research credit: P. Xu et al.; via Science News; submitted by Kam-Yung Soh)

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    Columbia Glacier’s Retreat

    In southeastern Alaska, the Columbia Glacier once stretched as far as Heather Island in Prince William Sound. After a long period of stability, the glacier began retreating in 1980 and currently sits more than 15 miles from its previous extent. This video explores the glacier’s evolution through false-color satellite imagery, which allows researchers to distinguish the glacier from sea ice, open water, exposed rocks, and nearby vegetation. Though rapid overall, the glacier’s retreat takes place in fits and starts, due to a combination of influences including climate change, sea and ice interactions, and the effects of local topography. (Video and image credit: NASA Earth Observatory)

    False-color animation showing the retreat of Alaska's Columbia Glacier since 1980.
    False-color animation showing the retreat of Alaska’s Columbia Glacier since 1980.
  • Dissolving Pinnacles

    Dissolving Pinnacles

    Limestone and other water-soluble rocks sometimes form sharp stone pinnacles like the ones seen here in Borneo. Scientists have recreated these structures in the laboratory simply by immersing water-soluble substances (essentially blocks of candy) into water. Without any background flow, the blocks will slowly form these pinnacle forests as material dissolves into the nearby water, creating a heavy solute-rich fluid that sinks down the exterior of the block. The convection generated by this dissolution drives the material into these sharp shapes, as shown mathematically in this recent study. (Image credit: N. Naim; research credit: J. Huang and N. Moore; via APS Physics)

  • “Oil Paintings”

    “Oil Paintings”

    To capture his images of auroras, nebulas, and comets, photographer Juha Tanhua points his camera lens downward, not upward. Despite their astrophysical appearance, Tanhua’s “oil paintings” are actually parking lot oil spills. The stars are roughened bits of asphalt, and the colors come from thin film interference in a layer of oil (similar to the way colors appear in soap bubbles). It’s amazing how much beauty he captures in examples of urban pollution. (Image credit: J. Tanhua; via Colossal)

  • Erie Ice

    Erie Ice

    Lake Erie, the shallowest of the Great Lakes, sees large swings in ice cover over the winter. In late January 2022, the lake was nearly completely frozen over, with 94 percent of its area covered in ice. By February 3rd, ice cover had dropped to 62 percent before rising again to 90 percent by the 5th. Air temperature and wind are the primary drivers of Erie’s fast ice growth and decay. As storms roll through, the ice can spread rapidly, but once temperatures rise, it takes very little forcing from the wind for the ice to begin breaking up. (Image credit: J. Stevens/USGS; via NASA Earth Observatory)

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    Burning Virtual Forests

    Wildfires are growing ever more frequent and more destructive as the climate crisis worsens. Unfortunately, simulating and predicting the course of these fires is incredibly difficult, requiring a combination of ecology, meteorology, combustion science, and more. To handle so many variables, model builders often turn to statistics that allow them to simulate an entire forest but at the cost of representing individual trees as a few pixels or a cone.

    In this video, researchers show a new wildfire simulation based on a computationally efficient but more realistic depiction of trees. With individual, three-dimensional trees, the simulation can capture effects that are otherwise hard to examine – like the difference in burn rate for coniferous and deciduous forests and the likelihood that a fire can jump a firebreak of a given size. Their weather, fire, and atmospheric models are even able to simulate the birth of fire-generated clouds! Check out the full video to see more and then head over to their site if you’d like to dig into the methodology. (Video and research credit: T. Hädrich et al.; see also)