FYFD

Category: Phenomena

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    Slow Mo Pulse Jet Engine

    Pulse jet engines rely on their shape to maintain combustion without moving parts. The pressure waves that travel through the engine pump fresh oxygen into the combustion chamber and then ignite it with exhaust remaining from the last cycle. In this Slow Mo Guys video, we get to see that process in action. It’s a pretty neat view of combustion in a working engine, but these guys are definitely not going to win any awards for safety measures. Seriously, don’t try this at home! (Image and video credit: The Slow Mo Guys)

  • Eyes on the Sun

    Eyes on the Sun

    Though it may look like the Eye of Sauron, this image is actually one of our best-ever glimpses of a sunspot. Captured by the Daniel K. Inouye Solar Telescope, this sunspot is larger than our entire planet, yet we can see details as small as 20km across. The dark central region of the image is the sunspot’s umbra, surrounded by the lighter, streakier penumbra. Along the edges of the image, you see a more typical pattern of bright convection cells. Compared to the rest of the sun’s surface, sunspots are cool — about 1,000 K cooler — due to their intense magnetic field flux inhibiting convection. (Image credit: NSO/AURA/NSF; via Bad Astronomer; submitted by Kam-Yung Soh)

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    The Strangeness of Sand

    Sand and other granular materials can flow, jam, and transmit forces in counterintuitive ways. This Lutetium Project video gives a nice overview of some of these bizarre properties.

    Many of sand’s odd characteristics come from the way forces move through grains that touch. Around 5:20 there’s a demo of one of these effects: the Janssen effect. Using a scale, the video shows the mass of a bunch of grains. Then, the host pours those grains into a narrow cylinder. If you watch the scale, you’ll see that it shows a smaller mass than before. That’s not because of a difference in mass between the bowl and the cylinder; the scale is calibrated to only measure the mass of the grains. In the narrow cylinder the grains appear to weigh less because part of their weight is being supported by force chains that run to the container’s walls. (Image and video credit: The Lutetium Project)

  • Aging Fluids

    Aging Fluids

    If you’ve ever left a sealed container of Playdoh untouched for months, you know that there’s a big difference between the fresh stuff and what’s left in that can. Aging can have big effects on non-Newtonian fluids. In this video, we see drops of a synthetic clay impacting at different speeds. In the top row of images, the clay is fresh and unaged; on impact, the clay forms large crown-like splashes. In the bottom row, however, the aged clay behaves quite differently. Instead of a splash, the drops make more of a splat. (Image and video credit: R. Ewoldt et al.)

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    Rolling Off a Duck’s Back

    Ducks and other water fowl need protection from the elements. Fortunately for them, the structure of their feathers cleverly helps them shed water. As seen in this video, feathers have tiny hooks, called barbicels, that act like Velcro, zipping the individual barbs of a feather together to keep water out. When birds preen, they’re using their bills to rezip any sections that came loose. They also use their bills to spread a waxy substance onto the feathers to give them even more waterproofing. All together, these measures help the birds keep out cold water and trap warm air in the down near their skin. (Image and video credit: Deep Look)

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    The Greedy Cup in Your Washing Machine

    A Pythagorean, or “greedy” cup, is one that automatically drains itself once filled to a certain level. In other words, it’s a self-starting siphon – one that triggers only at certain fill level. And chances are you have an example of this mechanism close at hand: inside your washing machine’s soap tray. That’s why the tray has such a clearly marked maximum fill line; if you were to put more soap than that in the tray, it would automatically drain! (Image and video credit: S. Mould)

  • Curls Past the Canaries

    Curls Past the Canaries

    When winds flow past a solitary peak, like an island in the ocean, they’re disrupted into a series of counter-rotating curls. That’s what we see here stretching to the southwest of Madeira Island. The official name for this flow is a von Karman vortex street, and it can be found anywhere from a soap film to a starship. (Image credit: J. Stevens; via NASA Earth Observatory)

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    The Colors of a Thin Film

    Soap bubbles and other thin films are colorful thanks to wave interference across their tiny thickness, but you may have noticed that only some colors appear. Others, like red, seem to be missing. In this video, Dianna digs into the details of wave interference and color theory to explain why we don’t see pure colors in a bubble.

    As she points out near the end of the video, the way to make a red bubble is to shine purely red light on the bubble, but even then, you’ll see stripes on it related to the light’s wavelength. Scientists actually use this property to measure the thickness of tiny air gaps between a droplet and a surface. (Image and video credit: Physics Girl)

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    Why Masks Cut COVID-19 Transmission So Well

    Face masks are an important tool for curtailing disease transmission, and this video explains how even imperfect masks do a much better job of protecting people than you may think. Strictly speaking, this video is not fluid dynamical — fluid dynamics plays more of a role in the details of what makes a mask effective — but the video is so good and so timely that I just have to share it. Given it a watch and then go explore the interactive essay to get an even better handle on mask mathematics. (Image and video credit: Minute Physics; see also The Multiplicative Power of Masks)

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    An Intro to Liquid Crystals

    There’s a good chance that the screen you’re using to read this uses liquid crystals, but how much do you know about this ubiquitous technology? Liquid crystals are fluids made up of molecules that orient into crystalline structures. Their usefulness for displays comes from the way they interact with light, changing the polarization of light based on their orientation. This Lutetium Project video is a great introduction to liquid crystals and some of their important properties, and, as always with LP videos, the journey is a beautiful one. (Image and video credit: The Lutetium Project)

    Want to learn how to promote your research in traditional media and online? This Friday Tom Crawford and I are presenting a free webinar on the topic as part of the Fluid Mechanics Webinar Series. Be sure to register ahead of time for the link and tune in at 4pm GMT (11am EST) on Friday. See you there!