FYFD

Tag: physics

  • Fast-Switching Multi-Material 3D Printer

    Fast-Switching Multi-Material 3D Printer

    For 3D printers to reach their potential, they need to handle more than one material and be able to swap quickly and seamlessly between them. That’s a tall order given how different materials like silicone and wax are. But a new 3D printer tackles that challenge using microfluidic nozzles designed extrude multiple fluids in quick succession. 

    The nozzle controls which fluid it ejects by pressurizing individual fluids, allowing it to switch from one to another up to 50 times a second (first image). Multiple nozzles, each containing multiple fluids, can be used to print periodically-patterned designed more quickly than previously possible (second image). The system can even directly print air-powered robots with both soft and hard components (third image). (Image and video credit: Nature, with M. Skylar-Scott et al.; research credit: M. Skylar-Scott et al.; via Nature; submitted by Kam-Yung Soh) 

  • Wave Clouds in the Front Range

    Wave Clouds in the Front Range

    Last Sunday night metro Denver was treated to a rare sight: clouds resembling breaking waves formed near sunset. These are Kelvin-Helmholtz clouds, and the comparison to ocean waves is apt, since the same physics is behind both. Winds were unusually calm near the ground Sunday night, but strong winds blew at the altitude just above the lower cloud layer. That velocity difference created strong shear where the two air layers met. With the cloud layer in place to differentiate the slower-moving air from the faster, we can what’s normally invisible: how the two air layers mix.

    The Denver Post has several more views of the wave clouds from around the area, and you can learn lots more about the Kelvin-Helmholtz instability here. (Image credit: R. Fields; via the Denver Post)

  • Finding New States of Matter

    Finding New States of Matter

    As children we’re taught that there are three basic states of matter: solids, liquids, and gases. The latter two are known scientifically as fluids. But the world doesn’t divide quite so simply into those three categories, and scientists have since named several other states of matter, including plasmas, superfluids, and Bose-Einstein condensates.  Many of these types of matter only exist under extreme temperatures and/or pressures, which makes them difficult to observe. Scientists have instead turned to numerical simulation to discover and study these exotic materials.

    One of the latest discoveries among these bizarre materials is a form of potassium that simultaneously displays properties of a solid and a liquid. Inside this so-called chain-melted potassium, there’s a complex crystalline lattice containing smaller chains of atoms. One author described the material thus: “ It would be like holding a sponge filled with water that starts dripping out, except the sponge is also made of water.” That certainly boggles my mind! (Image credit: Turtle Rock Scientific; research credit: V. Robinson et al.; via NatGeo; submitted by Emily R.)

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    Coke and Butane Rockets

    Rocket science has a reputation for being an incredibly difficult subject. But while there’s complexity in the execution, the concept behind rockets is pretty simple: throw mass out the back really fast and you’ll move forward. Whether you’re talking about a Saturn V or these Coke-and-butane-powered bottles, the basic principle is the same.

    These rockets get their kick mostly from the added butane, which has a very low boiling point. When the bottle is flipped, the lighter butane is forced to rise through the Coke. With a large surface area of liquid butane exposed to the warmer Coke, the butane becomes gaseous. That sudden increase in volume forces a liquid-Coke-and-gaseous-butane mixture out of the bottle, which has a helpful nozzle shape to further increase the propellant’s speed. Once the phase change is underway, the rocket quickly takes off! (Image and video credit: The Slow Mo Guys)

  • Making Drops Stick

    Making Drops Stick

    As you may have noticed when washing vegetables, many plants have superhydrophobic leaves. Water just beads up on their surface and slides right off. This is a useful feature for plants that want to direct that water toward their roots, but it’s a frustration in agriculture, where that superhydrophobicity means extra spraying of pesticides in order to get enough to stick to the plant.

    But that may not be the case for much longer. Researchers have found that adding a little polymer to water droplets (right) can suppress their ability to rebound (left) from superhydrophobic surfaces. Above a critical concentration, the high shear rate of the droplet as it tries to detach activates the viscoelastic properties of the polymer. That viscoelasticity suppresses the rebound, keeping the droplet attached. That’s good news for everyone, since it means less spraying is needed to protect crops. (Image and research credit: P. Dhar et al.)

  • Whiskey Stains

    Whiskey Stains

    Complex fluids leave behind fascinating stains after they evaporate. We’ve seen previously how coffee forms rings and whisky forms more complicated stains as surface tension changes during evaporation drive particles throughout the droplet. Now researchers are considering the differences between traditional Scottish whisky, which ages in re-used, uncharred barrels, and American whiskeys like bourbon, which are required to age in new, charred white oak barrels.

    When diluted, the American whiskeys form web-like patterns – seen above – that vary from brand to brand, like a fingerprint. The charring of the barrels allows American whiskeys to pick up more water-insoluble molecules compared to whisky aged in uncharred barrels. Since the webbed patterns form in American whiskey but not Scotch whisky, it’s likely those molecules play an important role in the evaporation dynamics and subsequent staining. (Image credit: S. Williams et al.; research credit: S. Williams et al.; via APS Physics; submitted by Kam-Yung Soh)

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    “Mocean”

    Ocean waves are endlessly fascinating to watch. In “Mocean,” cinematographer Chris Bryan captures them in ways few ever see, thanks to his high-speed camera. Honestly, this film is so gorgeous that I don’t want to distract you with the science, so just go watch!

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    All done? Pretty wonderful, right? There’s nothing quite like seeing those holes break and expand through sheets of water, tearing what looked solid into a spray of droplets that bleed salt into the atmosphere. Or how about those rib vortices underneath the waves? Or the cloud-like turbulence of the waves breaking overhead? How fortunate we are to see and capture and share such beauty! (Video and image credit: C. Bryan; via RedShark; submitted by Michael F.)

  • Leidenfrost Stars

    Leidenfrost Stars

    Atop a very hot surface, liquids can instantly vaporize, leaving a drop levitating on a layer of its own vapor. These Leidenfrost droplets demonstrate all kinds of interesting behaviors, including self-propulsion, explosion, and star-shaped oscillations, like those above. The oscillation is driven by feedback between the drop and its vapor layer. 

    Interestingly, the drops are capable of sustaining more than one mode of oscillation at once, as seen above. The obvious mode (m=5) corresponds to the 5 star-like points pushing out on the drop. But notice that the drop is also stretching into an oval shape that moves up and down, back and forth. This is the second mode (m=2) present. It moves slower than the m=5 mode, completing a cycle only once for every four cycles the other has. (Image and research credit: J. Bergen et al.)

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    Driving Instabilities with a Twist

    Imagine that you want to study how two fluids mix when a lighter fluid is pushed into a denser one. Conceptually, it’s a straightforward situation. It would be like having a layer of oil under a layer of water and watching what happens. But how do you do that experimentally? Oil won’t naturally stay under water. If you flip the container over to start the experiment, you’ve added a bunch of extra motion from the rotation. And if you use a barrier to separate the two layers and then pull it out, you’ve added extra shear where they meet.

    To deal with challenges like these, researchers at Lehigh University spent five years designing and building the rotating wheel apparatus you see in the video above. Instead of relying on gravity to force the lighter fluid into a denser one, this set-up uses centrifugal force. The test fluids start out on the loading wheel, spinning in their naturally stable configuration. Then once both sides are rotating at the desired speed, the track flips, transferring the experiment onto the other wheel, which rotates in the opposite sense. This gives the fluids a sudden change in the direction of the centrifugal force and, once the apparatus completes shake-down, should give us new insight into the sort of mixing seen in fusion. (Video credit: Lehigh University; see also Turbulent Flow Design Group)

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    Modeling Oobleck

    Oobleck – that peculiarly behaved mixture of cornstarch and water – continues to be a favorite of children and researchers both. Oobleck flows like a liquid when deformed slowly, but try to move it quickly and it will seize up like a solid. This sudden change depends on the tiny particles of cornstarch suspended in the liquid. When they’re given time, electrostatic forces between the particles help them repel one another and keep the liquid flowing. But under sudden impacts, the particles get jammed together and the friction between neighboring grains makes the viscosity of the fluid increase by orders of magnitude. 

    Researchers are now able to model these particle interactions numerically, which will help them predict how oobleck and similar substances will behave in applications like body armor or pothole repair. (Video credit: MIT; via MIT News; research credit: A. Baumgarten and K. Kamrin)