FYFD

Tag: physics

  • Finding New Shapes in Foam

    Finding New Shapes in Foam

    In the summer of 2018, a group of researchers announced they’d discovered a new geometrical shape, the scutoid. They found the scutoid, a sort of twisted prism, in the shape of epithelial cells packed between curved surfaces. Having heard of this new geometry, a different group of physicists wondered if they could find scutoids elsewhere, specifically, in the cells of a foam. As shown in the picture above, they did.

    To visualize a scutoid, first image a prism. Take two polygons with an equal number of sides and connect them. But if you imagine packing such prisms between two curved surfaces, you’ll quickly see that it won’t work. They just don’t fit together. Instead, one face may adopt, say, six sides, while the other takes on five. To join those two end faces, one of the sides will have to have a Y-shaped junction and a triangular face. This is a scutoid.

    You can see two such shapes in the image above. In the left bubble, the far side forms a pentagon, while the near face is a hexagon. On the right, the bubble has six faces in the background and eight in the foreground. And between them, you can just see the triangular face that connects the two scutoids.

    It’s not only exciting to find scutoids in a new, non-biological medium; it suggests a physical mechanism behind their formation. Foams are a well-known example of energy minimization. The fact that scutoids are found in a curved foam suggests that the shape itself is connected to energy minimization, something that could help us understand how biological scutoids grow and form. (Image and research credit: A. Mughal et al.; via Physics World; submitted by Kam-Yung Soh)

  • Vortices and Ground Effect

    Vortices and Ground Effect

    Though typically unseen, the vortices that swirl from the tips of aircraft wings are powerful. Here you see a Hawker Sea Fury equipped with a smoke system used to visualize the vortices that form at the wingtip as high-pressure air from the bottom of the wing and low-pressure air from the top swirl together. As you can see, the vortices persist in the wake long after the plane passes. The size and strength of the vortices depend on the size and speed of the aircraft; this is why air traffic control requires smaller planes to wait longer to take off or land if there was just a larger aircraft on the runway.

    The other cool thing to note here is how the wingtip vortices move apart from one another in the animation above. In flight, wingtip vortices usually stay roughly parallel to one another, but they drift downward in the aircraft’s wake. Near the ground, though, the vortices cannot move down, so instead ground effect forces them apart from one another, as seen here. (Image and video credit: E. Seguin; via Kelsey C.)

  • Sniffing Underwater

    Sniffing Underwater

    Star-nosed moles – tiny mammals native to the northeastern United States – have an underwater superpower: sniffing. To seek prey underwater, the moles blow bubbles and suck them back into their nostrils in about a tenth of a second. Their eponymous noses seem to be key to this, as seen in newly published research. Researchers built model star noses from plastic (lower right) to explore how well different shapes could hold the bubble in place, a necessary ingredient for the mole to sniff them back up. 

    With a perfectly flat plate, any small tilt makes the bubble slide toward the edge and float away. Star-shaped ones, on the other hand, can hold a bubble even up to a 7-degree tilt angle, a 40% improvement. The spacing of the gaps is also important. If they’re too wide, buoyancy can pull the bubble up through them. But if they’re too narrow for the bubble to deform upward through them, they make poor anchors. 

    Understanding the mechanics of underwater sniffing is good for more than just appreciating this funny-looking mammal, though. The researchers hope their findings will help develop underwater chemical sensors that use bubble sniffing instead of exposing their components directly to sea water, which would significantly extend their usable life. For more, check out the paper and my interview with the lead author in the video below. (Image credits: top and lower left – K. Catania; lower right – A. Lee; research credit: A. Lee and D. Hu; video credit: N. Sharp and T. Crawford)

  • Stress Between Grains

    Stress Between Grains

    Granular materials like sand and beads can shift and flow in fluid-like ways, but they’re much harder to predict. Part of this is due to the way friction between individual grains transmits force through the network. Here, we see photoelastic beads responding to the intrusion of a narrow rod. The lightning-like flashes show how stress is traveling between neighboring grains. Notice how the lower grains are essentially frozen into a state of high stress, but the movable upper grains shift and readjust themselves to try and relieve stress.

    This experiment took place under lunar gravitational conditions. Lower gravity means that it takes a larger pile of grains on top to create a given stress. But it also means it’s easier for those movable top grains to shift or even get thrown up by a hastily applied force.  The purpose of experiments like this is to better understand how rovers and probes should dig in low-gravity environments without kicking up a cloud of regolith and dust. (Image credit: K. Daniels et al., source)

  • The Best of FYFD 2018

    The Best of FYFD 2018

    2018 was a busy year for me with over 40 days of business travel, 10 invited talks, and a whole slew of new YouTube videos on top of regular FYFD posts. But now it’s time for the traditional look back at the top 10 FYFD posts of 2018, according to you:

    1. Swimming so easy a dead fish can do it
    2. The wall of lava lamps that helps secure the Internet
    3. Jellyfish versus vortex ring
    4. Crushing crayons in a hydraulic press shows off the sharkskin instability
    5. Vortex ring from an exploding meteor
    6. Starburst patterns form when avalanching materials size separate 
    7. Kelp change shape depending on their currents
    8. The creepy hydraulics of a spider’s gait
    9. Pneumatically-driven, 3D-printed plants of the future
    10. Exothermic chemistry visualized in infrared

    This year’s list is an interesting mix – some biology, vortex rings, non-Newtonian and granular physics; it’s a good list for some of the more unexpected sides of fluid dynamics. 

    If you’d like to see more great posts like these, please remember that FYFD is primarily supported by readers like you. You can help support the site by becoming a patron, making a one-time donation, or buying some merch. Happy New Year!

    (Image credits: fish – D. Beal et al.; lava lamps – T. Scott; vortex ring – V. de Valles; crayons – Hydraulic Press Channel; meteor – P. Horálek; rotating drum – I. Zuriguel et al.; kelp – J. Hildering; spider – R. Miller; hydrophytes – N. Hone; chemistry – Beauty of Science)

  • Waves

    Waves

    Photographer Ray Collins is known for his striking portraits of waves, some of which I’ve featured on previous occasions. Collins is colorblind, so he focuses heavily on shape and texture in the wave, which produces some stunningly dramatic views of moving water frozen in time. There’s great power and beauty in breaking waves, and researchers are still actively learning just how significant they are to our planet’s cycles. 

    Note the spray blurring the edges of every wave here; these are some of the largest droplets the wave will make. As it crashes forward, the wave traps pockets of air, and, as those bubbles burst, they will create a spray of tinier droplets that carry moisture and salt into the atmosphere to seed clouds and, eventually, rain.

    Collins’ work reminds us both of the ocean’s power and its fragility as it undergoes rapid changes due to humanity’s influence. For more photos as well as a great interview with Collins, check out My Modern Met. (Image credit: R. Collins; via My Modern Met and James H.)

  • Entrained

    Entrained

    When an object hits water whether it draws air in with it depends on its shape, impact speed, and surface characteristics. In this experiment, though, there’s a bit of a twist. Here the sphere is passing through an interface with surfactants added. On the left, the sphere passes through smoothly without entraining air or creating a cavity. On the right, the same sphere impacts at the same speed but this time the interface is covered in a layer of bubbles. As a result, the sphere pulls a large air cavity into the water with it. Why the big difference?

    As the sphere passes through the bubbles, they burst, spraying the sphere with droplets. On impact, those droplets disrupt the layer of water traveling up the sides of the sphere, causing it to pull away from the surface and form a splash. Instead of smoothly coating the sphere in water, air can now stick to the sphere and get pulled in with it. (Image and research credit: N. Speirs et al., source)

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    “Haboob”

    Mike Olbinski’s latest storm chasing timelapse, “Monsoon V,” is once again spectacular. Although I do think the name could have been “Haboob” instead, given how many sweeping dust clouds encroach on the viewer. These towering wall clouds of dust can form from downdrafts at the leading edge of a cold front, or from the fading remains of a thunderstorm. In dry, dusty regions like Arizona, the strong downward winds spread outward as they near the ground, picking up dust and sand. Below you can see two examples of haboobs racing ahead of fronts. 

    The middle image shows a microburst, where a sudden, localized downdraft falls out of the storm. Notice how the wind and rain sweep outward as they near the ground. This is typical of any flow heading straight toward a wall! Check out the full video for lots more gorgeous fluid dynamics in action. (Video and image credit: M. Olbinski)

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    Fire Tornado in a Bubble

    File this one under awesome tricks you shouldn’t try at home. Here bubble artist Dustin Skye demonstrates his handheld inverted fire tornado. First, he blows a large encapsulating bubble, then blows butane and smoke into a smaller secondary bubble. When he breaks the wall between the two, the mixture swirls into the larger bubble. Then, by breaking a narrow hole into the remaining bubble, Skye forms a swirling tornado. He’s using conservation of angular momentum here to concentrate the vorticity he created by blowing into the original butane bubble. As the big bubble shrinks, the vorticity inside gets pulled inward and speeds up – like when a spinning ice skater pulls his arms in. That’s how you get the tornado. And from there, it’s just a matter of lighting the exiting butane and air mixture. (Video credit: D. Skye; via Gizmodo)

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    “Winter’s Magic”

    Don Komarechka’s beautiful short film, “Winter’s Magic,” captures the beauty of soap bubbles as they freeze. It’s a delicate process and one difficult to capture in video. The bubble freezes first at the bottom, where it touches the cold surface – in this case, snow. That freezing releases latent heat and creates a temperature gradient along the thin liquid film. With that temperature gradient comes a variation in surface tension, and it’s this that creates the flow that lifts the ice crystals from the surface and turns the bubble into a snow globe. Eventually, as the frozen crystals continue growing, flow in the bubble walls comes to halt as the film solidifies.

    For more on the physics of freezing bubbles, check out this interview with the researchers, or, to learn more on how to film freezing bubbles, check out Komarechka’s description. (Video and image credit: D. Komarechka; via Laughing Squid; h/t to Jennifer O.)