FYFD

Tag: physics

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    Why Watering Globes Are Hard to Fill

    If you’re leaving home for a few days and want to keep your houseplants happy, you may have tried using a watering globe – those glass bulbs with long stems that slowly release water for your plant. And if you have used one, you’ve probably noticed what a pain it can be to fill. Pour water down the neck too quickly and you’ll get splashed by a sheet of water blown back at you.

    That splashback happens for the same reason that blowing across the top of a bottle plays an audible note: you’re compressing the air inside the container. When water tries to pour continuously down the watering globe’s neck, it can block the escape path needed by the air already in the globe. The increasing weight of water atop that volume of air compresses it, raising its pressure until it’s eventually high enough that it blows all the water back out the neck and into your face.

    The best method to ensure that doesn’t happen is to fill the globe slowly. Try tilting it at an angle and letting only a small stream of water fall into it such that there’s always an escape route for the air. (Image and video credit: E. Challita et al.)

  • Oil Drops and Filter Feeders

    Oil Drops and Filter Feeders

    Natural oils provide critical nutrients to filter feeders like zooplankton and barnacles. These creatures capture oil droplets on bristle-like appendages such as cilia and setae. But this droplet-catching turns into a disadvantage during petroleum spills, when capturing and ingesting oil can be lethal. A recent study looks at the fluid dynamics of oil droplet capture for these tiny creatures.

    The authors found that filter feeders capture a range of droplets regardless of size and oil viscosity. But not all droplets stay attached long enough to get consumed, and the larger a droplet is, the lower the flow velocity necessary to detach it from the animal. That suggests a method of limiting uptake of spilled petroleum into the marine food chain: use surfactants to break up the oil into droplets large enough that they’ll detach from filter feeders before getting eaten. (Image credit: D. Pelusi; research credit: F. Letendre et al.; submitted by Christopher C.)

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    Hot Ice, Buoyancy Tricks, and More DIY Fun

    Here’s a smorgasbord of DIY experiments from Dianna at Physics Girl. Some are fluidsy, some aren’t, but all of them give you a chance to stretch your science muscles at home. Personally, I think she saved the best for last with her laser-acoustics demo! (Video credit: Physics Girl)

  • Testing Granular Gas Theory

    Testing Granular Gas Theory

    When excited, a group of particles can behave much like a gas. These granular gases exhibit many similarities to molecular gases but contain one vital difference: without a constant input of energy, granular gases lose kinetic energy to collisions.

    Over the years, scientists have developed a special theory to describe the behaviors of granular gases, but most of its predictions could only be tested numerically. A new study used a microgravity experiment aboard a sounding rocket to physically test the theory.

    The experiment, shown above, consists of nearly 2800 magnetic particles, which the researchers could stir up using pairs of magnets. Once they shut off the magnets (which occurs at t=0 in the image above), the granular gas begins to “cool” as collisions sap away its energy. With this set-up, the researchers were able to confirm several key predictions of the granular gas theory. (Image and research credit: P. Yu et al.; via APS Physics)

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    Centrifugal Instability

    When it comes to geophysics, there are all kinds of phenomena that depend on rotation. In this short video, researchers demonstrate one such phenomena — the centrifugal instability — in a tank on a turn table. The experiment begins once the fluid in the tank is all rotating together, like a solid body would. Then, they reduce the rotation rate of the turn table. Almost immediately, we see rolls encircle the tank.

    The rolls form due to the difference in momentum between fluid in the interior and near the wall. Friction with the wall slows the fluid there down much faster than that in the middle of the tank. As the faster-moving fluid gets centrifuged outward, it forms rolls. As the video demonstrates, these rolls can be relatively uniform and laminar, or, with enough change in rotation rate, they can become turbulent. (Image and video credit: UCLA Spinlab)

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    Dendritic

    “What happens when two scientists, a composer, a cellist, and a planetarium animator make art?” The answer is “Dendritic,” a musical composition built directly on the tree-like branching patterns found when a less viscous fluid is injected into a more viscous one sandwiched between two plates.

    Normally this viscous fingering instability results in dense, branching fingers, but when there’s directional dependence in the fluid, the pattern transitions instead to one that’s dendritic. In this case, that directionality comes from liquid crystals, whose are rod-like shape makes it easier for liquid to flow in the direction aligned with the rods.

    For more on the science, math, and music behind the piece, check out this description from the scientists and composer. (Video, image, and submission credit: I. Bischofberger et al.)

  • 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)

  • Bacterial Turbulence

    Bacterial Turbulence

    Conventional fluid dynamical wisdom posits that any flows at the microscale should be laminar. Tiny swimmers like microorganisms live in a world dominated by viscosity, therefore, there can be no turbulence. But experiments with bacterial colonies have shown that’s not entirely true. With enough micro-swimmers moving around, even these viscous, small-scale flows become turbulent.

    That’s what is shown in Image 2, where tracer particles show the complex motion of fluid around a bacterial swarm. By tracking both the bacteria motion and the fluid motion, researchers were able to describe the flow using statistical methods similar to those used for conventional turbulence. The characteristics of this bacterial turbulence are not identical to larger-scale turbulence, but they are certainly more turbulent than laminar. (Image credits: bacterium – A. Weiner, bacterial turbulence – J. Dunkel et al.; research credit: J. Dunkel et al.; submitted by Jeff M.)

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    How Canal Locks Work

    For thousands of years, boats have been a critical component of trade, efficiently enabling transport of goods over large distances. But water’s self-leveling creates challenges when moving up and downstream through rivers and canals. To get around this, engineers use locks, which act as a sort of gravity-driven elevator to lift and lower boats to the appropriate water level. In this video from Practical Engineering, we learn about the basic physics behind locks as well as some of the methods engineers use to limit water loss through the lock. (Image and video credit: Practical Engineering)

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    Fluorescent Dancing Droplets

    These fluorescent droplets of glowstick liquid jiggle and dance in a solution of sodium hydroxide. Some droplets jitter. Some rotate. And some undergo one coalescence after another. It’s always fun to see how fluid dynamics and chemistry combine! (Image and video credit: Beauty of Science)