FYFD

Search results for: “droplet”

  • Bright Volcanic Clouds

    Bright Volcanic Clouds

    Every day human activity pumps aerosol particles into the atmosphere, potentially altering our weather patterns. But tracking the effects of those emissions is difficult with so many variables changing at once. It’s easier to see how such particles affect weather patterns somewhere like the Sandwich Islands, where we can observe the effects of a single, known source like a volcano.

    That’s what we see in this false-color satellite image. Mount Michael has a permanent lava lake in its central crater, and so often releases sulfur dioxide and other gases. As those gases rise and mix with the passing atmosphere, they can create bright, persistent cloud trails like the one seen here. The brightening comes from the additional small cloud droplets that form around the extra particles emitted from the volcano.

    As a bonus, this image includes some extra fluid dynamical goodness. Check out the wave clouds and von Karman vortices in the wake of the neighboring islands! (Image credit: J. Stevens; via NASA Earth Observatory)

  • Featured Video Play Icon

    Ventilation and Respiratory Disease

    In 1977, one passenger with the flu infected 38 people onboard a flight with malfunctioning ventilation. In this video, Dianna digs into the physics of respiratory disease transmission and just why ventilation is so key to preventing it.

    There are three primary modes of transmission for respiratory diseases like influence or SARS-CoV-2: 1) touching an infected surface and then oneself, i.e., self-inoculation; 2) inhaling virus-filled droplets larger than 5 nm; and 3) inhaling virus-filled droplets smaller than 5 nm. That size cut-off may seem a little arbitrary, but it’s how scientists distinguish between droplets that fall quickly to the ground and ones that can persist on buoyant air currents.

    That airborne persistence is one of the reasons ventilation — in other words, replacing the air — is so important. So many people on that 1977 flight got sick because there was no system removing the infected air and bringing in fresh air. For more on the fluid dynamics disease transmission, check out these posts. Curious about those bacterial bubble bursts? I’ve covered that, too. (Video and image credit: Physics Girl)

  • Featured Video Play Icon

    Sundews Weaponize Viscoelasticity

    In nutrient-poor soils, carnivorous plants like the cape sundew supplement their diets by eating insects. To entice their prey, the cape sundew secretes droplets of sugary water. But unwary insects who land to feed soon find themselves unable to pull away from this viscoelastic liquid. Complex molecules in the fluid grant it elasticity, so when insects pull against it, the liquid stretches and pulls back instead of breaking up. Other carnivorous plants, like the pitcher plant, use similar non-Newtonian tricks to trap insects. (Video and image credit: Deep Look)

  • Featured Video Play Icon

    Slow Mo Espresso

    High-speed photography gives us an alternate glimpse of reality. Here it provides an all-new perspective on making espresso. Surface tension plays a starring role, first in pulling together the film that forms over the exit, then in creating the drips and drops that follow. The break-up of espresso into individual droplets is an example of the Plateau-Rayleigh instability, where surface tension drives any wobble in the falling jet to pinch off. For more slow-motion espresso, you can also check out this behind-the-scenes video. (Video and image credit: J. Hoffmann; submitted by Jerrod H.)

  • Featured Video Play Icon

    Molten Thermite

    This glowing, molten liquid captured by the Slow Mo Guys is thermite. The chemical reaction behind thermite is highly exothermic, hence its intense glow. There’s some great fluid dynamics hiding in this video. First, there’s the dripping thermite (Image 1), which breaks up into droplets via the Plateau-Rayleigh instability before shattering when it hits the ground.

    Then there are the sequences (Images 2 and 3) of thermite dripping into water. The heat of the reacting thermite vaporizes a layer of water around it, creating a bubble that completely envelops the thermite. In other words, the falling thermite is supercavitating! That layer of air significantly reduces drag on the thermite and it insulates the thermite from the cooler temperature of the water. (Video and image credit: The Slow Mo Guys)

  • Featured Video Play Icon

    Popping an Oil Balloon

    Oil and water don’t mix — or at least they won’t without a lot of effort! In this video, we get to admire just how immiscible these fluids are as oil-filled balloons get burst underwater.

    Visually, the two bursts are quite spectacular. In the first image, the initial balloon has a sizeable air bubble at the top, which rises even more rapidly than the buoyant oil, creating a miniature, jelly-fish-like plume that reaches the surface first. The large oil plume follows, behaving similarly to the balloon burst without an added air bubble.

    The last of the oil in both cases comes from a cloud of smaller droplets formed near the bottom of the balloon. Being smaller and less buoyant, these drops take a lot longer to rise to the surface and remain much closer to spherical as they do. I suspect these smaller droplets form due to the forces created by the fast-moving elastic as it tears away. (Video and image credit: Warped Perception)

  • Featured Video Play Icon

    A Hand in Hot Oil

    In this video, Dianna from Physics Girl demonstrates a feat no one should try at home: dipping her hand into boiling oil. To stay safe, she’s relying on the Leidenfrost effect, the tendency of liquids exposed to temperatures well above their boiling point to vaporize and create a layer of gas that insulates against further heat transfer.

    We’ve seen a lot of cool behaviors from Leidenfrost droplets, like surfing on herringbone surfaces, digging through sand, vibrating like a star, and, well, violently exploding. We know a lot about what can happen in this Leidenfrost state, but there are also some major unknowns, like exactly what the Leidenfrost temperature is for many liquids. That’s part of what makes Dianna’s demo so dangerous; the temperature needed to see the Leidenfrost effect — even just for water — varies wildly depending on the experimental set-up. (Video and image credit: Physics Girl)

  • Featured Video Play Icon

    “Oooh !! My Delicious Coffee”

    I’m not a coffee person, but Thomas Blanchard’s “Oooh !! My Delicious Coffee” manages to capture my favorite part of the beverage – watching cream and coffee mix. From feathery flows driven by surface tension to droplets floating like miniature cappuccinos, the short film features many of the fantastical landscapes we find when staring into a coffee cup. But don’t get too eager to drink it; Blanchard used a combination of coffee, oil, and paint to achieve those effects! (Image and video credit: T. Blanchard)

  • Featured Video Play Icon

    How Well Do Masks Work?

    Many mixed messages have been spread about the efficacy of masks in preventing transmission of COVID-19. Nevertheless, there is good evidence that they help, as discussed in this video from It’s Okay to Be Smart. Much of the video shows schlieren imaging of a (healthy) individual engaging in regular activities – like talking, breathing, and coughing — with and without a cloth mask.

    Now, it’s important to note that what you see in these images is airflow, not the droplets that can carry the virus. However, research has shown that these airflows play a significant role in transporting droplets. It follows that disrupting those airflows can disrupt transmission of diseases passed via droplet. This is one of the key reasons to wear a mask.

    Notice how far jets and plumes of air fly from a maskless person’s mouth and nose. We cannot even observe how far momentum carries that air because the area visualized in this schlieren set-up is smaller than the full distance the air moves! But wearing a mask breaks up that flow structure. It reduces the air’s momentum, and it forces any air that does escape to move in smaller, less efficient structures. Even without considering any filtering effects or the fact that masks catch large droplets coming out of the wearer’s mouth, it’s clear that mask-wearing keeps others nearby safer. (Video and image credit: It’s Okay to Be Smart; references)

  • Shake It!

    Shake It!

    Vibrate a pool of water, and you’ll get Faraday waves, ripple-like excitations that form their own distinctive pattern compared to the driving vibration. But you don’t have to vibrate a pure liquid to see Faraday waves. A recent study observed them in vibrated earthworms!

    Odd as this may sound, the results make sense. When anesthetized (as they were in the experiments), earthworms are essentially a liquid wrapped in an elastic membrane, which is not so different from a droplet held together by surface tension.

    But why vibrate earthworms in the first place? It turns out earthworms are a good model organism for studies of vertebrate neural systems, so observing how vibrations propagate through them can provide insight into how our own nervous systems transmit information. (Image, research, and submission credit: I. Maksymov and A. Pototsky)

More posts