FYFD

Category: Phenomena

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    Spinning Water

    If you spin a tank of water at a constant speed, it takes on a curved, parabolic shape–a demonstration often called Newton’s bucket. Here, a team from UCLA shows how it’s done, both in terms of the equipment needed and a concise explanation of the physics. In the rotating experiment, water is subjected to both gravity (which acts in a constant magnitude across the tank) and centrifugal force (which is stronger further from the axis of rotation). The shape that balances these forces is a paraboloid, which is why the water takes on that shape. (Video and image credit: UCLA SpinLab)

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    Dispersing Pollutants via Smokestack

    In our industrialized society, pollutants are, to an extent, unavoidable. Even with technologies to drastically reduce the amount of pollutants leaving a factory or plant, some will still get released. It’s up to engineers to make sure that those released spread out enough that their overall concentration does not pose a risk to public health. In this Practical Engineering video, Grady explains some of the physics and engineering considerations that go into this task.

    As he demonstrates, taller smokestacks speed up the buoyant exhaust plume (to an extent), which exposes the plume to higher winds, greater turbulence, and, thus, quicker dispersal. But atmospheric conditions and even nearby buildings all affect how a plume spreads. (Image and video credit: Practical Engineering)

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  • A Braided River

    A Braided River

    The Yarlung Zangbo River winds through Tibet as the world’s highest-altitude major river. Parts of it cut through a canyon deeper than 6,000 meters (three times the depth of the Grand Canyon). And other parts, like this section, are braided, with waterways that shift rapidly from season to season. The swift changes in a braided river’s sandbars come from large amounts of sediment eroded from steep mountains upstream. As that sediment sweeps downstream, some will deposit, which narrows channels and can increase their scouring. The river’s shape quickly becomes a complicated battle between sediment, flow speed, and slope. (Image credit: M. Garrison; animation credit: R. Walter; via NASA Earth Observatory)

    Animation of the changing waterways of a braided river.
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    Seeking Randomness

    Securing information on the Internet requires a lot of random numbers, something computers are not good at creating on their own. This need for random input raises an important philosophical and practical question: what is randomness? How can we be sure that something truly is random, or is it enough for a system to be practically random? Joe explores these questions in this Be Smart video, which shows off how companies use systems — including fluid dynamical ones like lava lamps and wave machines — to generate random numbers for encryption. (Video and image credit: Be Smart)

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  • Rip Currents and Hurricanes

    Rip Currents and Hurricanes

    When it comes to the beach, looks can be deceiving. That calm-looking water to the side of big crashing waves may actually be a rip current that carries water back out to the ocean. Rip currents are a result of conservation of mass; just as waves carry water to the shore, something has to carry that incoming water back out to the ocean. Depending on the local topography, that outflow could be below the water surface, creating an undertow, or along the surface, as a rip current.

    Even when far offshore, hurricanes can trigger unexpected and strong rip currents, largely because they create bigger waves that travel shoreward. Those waves can also change the depth and layout of the underwater shoreline, potentially exacerbating rip currents.

    For more on rip currents, including the latest guidance on how to escape one, check out this article. (Image credit: A. Marlowe; via SciAm)

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  • Cooling Tower Demolition

    Cooling Tower Demolition

    As part of the demolition of a decommissioned coal-fired power plant in Nottinghamshire, workers simultaneously demolished eight cooling towers. The video is here. As the towers collapse, smoke and dust gets blown both out of the base and up each tower. The flow details are fascinating. The plumes have rings in them, perhaps related to how the blast’s waves reflect in the tower or how the structure itself fails. Vortex rings curl up as the rising plumes mix with the surrounding air. If you’re anything like me, you’ll have to replay it several times! (Image credit: BBC; submitted by jshoer)

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  • A Glimpse of the Solar Wind

    A Glimpse of the Solar Wind

    In December 2024, Parker Solar Probe made its closest pass yet to our Sun. In doing so, it captured the detailed images seen here, where three coronal mass ejections — giant releases of plasma, twisted by magnetic fields — collide in the Sun’s corona. Events like these shape the solar wind and the space weather that reaches us here on Earth. The biggest events can cause beautiful auroras, but they also run the risk of breaking satellites, power grids, and other infrastructure. (Image credit: NASA/Johns Hopkins APL/Naval Research Lab; video credit: NASA Goddard; via Gizmodo)

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    Damping a Skyscraper

    Wind forces on a skyscraper can set it swaying, so engineers design dampers to stop the motion and keep users comfortable. Some buildings use suspended solid mass dampers to counter a building’s motion, but others take a liquid approach. Whether by shifting water through specially shaped chambers or by sloshing it back and forth in a tank, a tuned liquid damper system can quickly bring a building back to rest. In this Practical Engineering video, Grady discusses the challenges of designing these systems and demonstrates how they work with a cool tabletop version. As a reminder, sloshing also helps in water-bottle flipping and stopping a bouncing ball. (Video and image credit: Practical Engineering)

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  • Thawing Out

    Thawing Out

    Lake Erie, the shallowest of the Great Lakes, can almost completely freeze over in winter. In this satellite image of the lake in March 2025, about a third of the lake remains ice-covered, while sediment — resuspended by wind and currents — and phytoplankton swirl in the ice-free zone. In recent decades, scientists discovered that diatoms, one of the phytoplankton groups found in the lake, can live within and just below Erie’s ice, thanks to a symbiotic relationship with an ice-loving bacteria. This symbiosis allows the diatoms to attach to the underside of the ice and gather the light needed for photosynthesis. Even in the depths of winter, an ice-covered lake can teem with life. (Image credit: M. Garrison; via NASA Earth Observatory)

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    How Particles Affect Melting Ice

    When ice melts in salt water, there’s an upward flow along the ice caused by the difference in density. But most ice in nature is not purely water. What happens when there are particles trapped in the ice? That’s the question this video asks. The answer turns out to be relatively complex, but the researchers do a nice job of stepping viewers through their logic.

    Large particles tend to fall off one-by-one, which doesn’t really affect the buoyant upward flow along the ice. In contrast, smaller particles fall downward in a plume that completely overwhelms the buoyant flow. That strong downward flow makes the ice ablate even faster. (Video and image credit: S. Bootsma et al.)

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