FYFD

Tag: physics

  • The Jumping Jump

    The Jumping Jump

    Turn on your kitchen sink, and the falling jet may form a circle of shallow flow where it strikes the sink. This fast-moving region of flow, surrounded by a wall of water, is a hydraulic jump. A recent study delves into a previously-missed phenomenon of this flow: intermittent disruption and reappearance.

    An oscillating hydraulic jump, viewed from below.
    An oscillating hydraulic jump, viewed from below.

    The team found that, within a narrow range of jet and surface sizes, a hydraulic jump will periodically appear and disappear. The effect comes from the hydraulic jump itself; waves from the jump propagate outward, hit the edge of the circular plate, and reflect inward. When the incoming and outgoing waves interfere, it floods the jump zone, making it disappear briefly. (Image credit: sink – Nik, jump – A. Goerlinger et al.; research credit: A. Goerlinger et al.; via APS Physics)

  • “Emerald Roots”

    “Emerald Roots”

    As charged particles from the solar wind bombard the upper atmosphere, a glowing plasma forms and dances in the sky. The green light of the plasma reflects off moistened sand, rippled by the passage of wind and tide. Each component seems simple, but this striking image contains hidden depths of fluid dynamics. Magnetohydrodynamics govern the aurora’s dance; the sand’s self-organization mirrors dune physics; and even the rocky outcropping in the background was carefully shaped by erosive forces from wind and water. Truly, fluid dynamics are found everywhere. (Image credit: L. Tenti; via 2023 Astronomy POTY)

  • Swedish Egg Coffee

    Swedish Egg Coffee

    In the mid-1800s, Scandinavian immigrants settling in the Midwest had no filters, no percolators, and no drip coffee makers to aid their quest for a cup of coffee. Instead, they used eggs to boil a smooth, grit-free cup. Mixing the coffee grounds with egg — sometimes with the shell and all — creates a protein-packed raft that floats when the coffee’s done boiling. Adding cold water sinks the raft of ground coffee, giving a clean final pour with no filter necessary. I’m not a coffee drinker, but for those of you who are, I’m curious: would you drink an egg coffee? (Image credit: K. Tomlinson; via Atlas Obscura; submitted by Richard B.)

  • Turbulent Thermal Convection

    Turbulent Thermal Convection

    In the winter, warm air rises from our floor vents or radiators, creating a complex, invisible flow in the background of our lives. Buoyancy lifts warmer air upward while cooler, denser air sinks back down. This thermal convection is everywhere: in our buildings, the ocean, the sky overhead — even in the visible layer of our sun.

    In nature, these systems are so large and complex that fully measuring or simulating them remains impossible. Instead, researchers focus on a simplified system — a Rayleigh-Bénard cell — that’s essentially an idealized version of a pot on a stovetop. The lower surface of the cell is heated — like the bottom of a pan on the burner — while the upper surface of the fluid cools. Even this idealized system is a challenge, though, and neither lab-scale versions nor simulations can reach the same conditions that we find in nature.

    To bridge the gap, scientists rely on mathematical models — theories built on our best understanding of the physics — and physical analogies to similar systems — like flow over a flat plate — that are “easier” to measure. For a thorough overview of recent work in the area, check out this review in Physics Today. (Image credit: A. Blass; research credit: D. Lohse and O. Shishkina in Physics Today)

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    A Working Wirtz Pump

    In the mid-eighteenth century, pewterer Andreas Wirtz invented a spiral pump. Even today, his design is useful for small-scale, low-power pumping, as seen in this Steve Mould video. The design relies on a series of air and water plugs to build up pressure that’s then used to lift the fluids higher. In the video, Mould visits a stream-powered, home version of a Wirtz pump that regularly delivers water over eight meters in elevation. See it in action in the full video! (Video and image credit: S. Mould)

  • Enhancing the Cheerios Effect

    Enhancing the Cheerios Effect

    The Cheerios in your morning cereal clump together with one another and the bowl’s wall due to an attractive force caused by the curvature of their menisci. A recent study looks at how this effect changes when you’re pulling objects out of the liquid.

    Snapshots show how two flexible fibers get drawn together by an attractive force as they are pulled out of silicon oil.
    Snapshots show how two flexible fibers get drawn together by an attractive force as they are pulled out of silicon oil.

    The researchers inserted thin flexible glass fibers into silicon oil and withdrew them. As they did, they explored what lengths and retraction speeds caused the fibers to pull together. They found that a single moving rod had a taller meniscus than a stationary one, and two moving rods had a liquid bridge that superposed their individual menisci. The result was an attractive force even stronger than what the fibers experienced when still. (Image credit: Cheerios – D. Streit, experiment – H. Bense et al.; research credit: H. Bense et al.; via APS Physics)

  • “A Sun Question”

    “A Sun Question”

    The sun‘s surface and atmosphere are endlessly dynamic, with magnetic lines, plasma, and convection creating a constant churn. In this photo by astrophotographer Eduardo Schaberger Poupeau, a curving question-mark-like filament appears above the sun’s surface. Even with decades of high-resolution data from recent solar probes, we struggle to understand the complex physics that feed structures like these. (Image credit: E. Poupeau; via 2023 Astronomy POTY)

  • Swirling Sea Ice

    Swirling Sea Ice

    The Sea of Okhotsk is the northern hemisphere’s southernmost sea that seasonally freezes. Caught between the Siberian coast and the Kamchatka Peninsula, cold air from Siberia helps freeze water kept at lower salinity due to freshwater run-off. This image, taken in May 2023, shows free-floating sea ice forming spirals driven by wind and waves. Small islands off the eastern coast (right side in image) are likely responsible for the swirling eddies seen there. Like phytoplankton blooms and sediment swirls in warmer seasons, the sea ice acts as a tracer to reveal flow. (Image credit: W. Liang; via NASA Earth Observatory)

  • Jamming Inside

    Jamming Inside

    Worm-like Spirostomum ambiguum are millimeter-sized single-cell organisms that live in brackish waters. In milliseconds, these cells can retract to half their original length, generating g-forces greater than a Formula One driver experiences when cornering. How, researchers wondered, do these cells avoid shredding their internal structure with forces that strong?

    Spirostomum ambiguum, they found, contain fluid-filled sacs called vacuoles that are entangled with the folds of a membrane-like structure called the endoplasmic reticulum. The researchers constructed a simulated cell, based on the properties of the living ones, and tested it under retraction. Without the endoplasmic reticulum, the insides of their model acted like a liquid, with vacuoles moving past one another readily. That’s not good for staying alive since swapping positions can disrupt bodily functions.

    An artificially-colored micrograph highlights the different structures inside Spirostomum ambiguum. The red strings are a membrane-like endoplasmic reticulum entangled between yellow, fluid-filled vacuoles.
    An artificially-colored micrograph highlights the different structures inside Spirostomum ambiguum. The red strings are a membrane-like endoplasmic reticulum entangled between yellow, fluid-filled vacuoles.

    With the vacuoles connected by a model endoplasmic reticulum, the cell’s insides acted more like a solid during retraction. The vacuoles deformed but fewer of them traded places, instead jamming together to prevent rearrangement. Mimicking this structure at a larger scale, the team suggests, could enable new types of shock absorbers. (Image and research credit: R. Chang and M. Prakash; via APS Physics)

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    Do Droughts Worsen Floods?

    In recent years many areas have seen record droughts followed by sudden, massive rainfalls. Such wild swings raise the question: does drought-parched soil make flooding worse? That’s the question Grady tackles in this Practical Engineering video, and, as is often the cause in real-world engineering, the answer is complicated.

    How quickly water soaks into the spaces between soil particles depends on many factors, including soil type, vegetation, and how much moisture is in the soil already. In general, dry soils initially soak water in more quickly than pre-moistened soil – except when the surface soil is hydrophobic and water-repellent. Check out the full video to learn more! (Video and image credit: Practical Engineering)