FYFD

Category: Phenomena

  • Featured Video Play Icon

    Coastal Erosion

    The same dynamic forces that make coastlines fascinating create perennial headaches for engineers trying to maintain coastlines against erosion. This Practical Engineering video discusses some of the challenges of coastal erosion and how engineers counter them.

    In a completely undeveloped coastline, waves and storms erode the shoreline while rivers and currents replenish sand through sedimentation. Manmade structures tend to strengthen erosion processes while disrupting the sedimentation that would normally counter it. Beach nourishment — where sand gets dredged up and deposited on a beach — is an engineered attempt to replace natural sedimentation.

    Dunes, mangrove forests, and wetlands are all nature’s way of protecting and maintaining coastlines. We engineers are still learning how to both utilize and protect shorelines. (Image and video credit: Practical Engineering)

  • Featured Video Play Icon

    Ultrasonic Vibrations

    Ultrafast vibrations can break up droplets, mix fluids, and even tear voids in a liquid. Here, the Slow Mo Guys demonstrate each of these using an ultrasonic homogenizer, a piece of lab equipment capable of vibrating 30,000 times a second. At that speed generating cavitation bubbles is trivial, and the flow induced by that cavitation is well-suited to emulsifying otherwise immiscible liquids like oil and water. They also show how a lone droplet gets torn into many microdroplets, a process formally known as atomization. (Image and video credit: The Slow Mo Guys)

  • Snowflake Velocimetry

    Snowflake Velocimetry

    In our era of remote learning, students don’t always have a chance to do hands-on lab experiments in the usual fashion. But that doesn’t mean they can’t explore important flow diagnostic techniques. Here a simple smartphone video of snow falling gets turned into a lesson on particle image velocimetry, or PIV, a major technique for measuring flow velocities.

    A nearby house acts as a fixed backdrop, and by comparing snowflake positions from one frame to the next, students can measure the instantaneous flow patterns in the snowfall. Of course, that’s a tedious task to do by hand, but luckily there are computer programs that do it automatically. Simply run the smartphone video through the software, and analyze the patterns it reveals!

    As a bonus, students don’t have to get distracted by the complexities of laser sheets and flow seeding that are normally a part of PIV. Instead, the flow and the lighting are already right outside their window, and they can concentrate instead on learning the principles of the technique and how to use the software. (Image and submission credit: J. Stafford)

  • Strings of Swirls

    Strings of Swirls

    Von Karman vortex streets are the rows of alternating vortices shed off isolated objects interrupting a flow. Here, the volcanic peaks of Cabo Verde disrupt an atmospheric flow accustomed to an empty ocean. In a steady wind, air wraps around the volcanoes and detaches first on one side, creating a vortex, then from the other side, making a vortex of the opposite rotation. Although these structures are always present, we only see them when they stir up the cloud layer, leaving these strings of swirls for hundreds of kilometers behind the islands. (Image credit: L. Dauphin/NASA; via NASA Earth Observatory)

  • Featured Video Play Icon

    Chasing Tornadoes

    Tornadoes are some of the most powerful storms on Earth. Their difficult-to-predict nature means that we still have a relatively scant understanding of exactly how they form. We know the conditions that promote their development — warm, moist rising air, wind shear, and rotation — but how and when those translate into a dangerous funnel cloud is harder to pin down. In this video, we hear from one of National Geographic’s storm researchers, Anton Seimon, who chases these storms in search of answers. (Image and video credit: National Geographic)

  • Featured Video Play Icon

    Permeable Pavement

    Controlling storm water is a major challenge in urban environments, where many surfaces are impermeable. In a city, rain cannot simply soak into the ground and filter into the water table. One potential solution is permeable pavement, which uses the same ingredients as its common counterpart minus the sand that usually packs into gaps between the gravel. Without the sand, the final pavement allows water to soak through, as seen above. In practice, the water sinks into a porous reservoir beneath the pavement that helps store and regulate the water’s discharge into the soil.

    Unfortunately, this solution has its limitations. Permeable pavement is not as strong as the regular variety, so it doesn’t work for highly trafficked areas like roadways. It’s also not well-suited to colder areas, where freezing and thawing may disrupt its operation. But it is another tool in engineers’ toolboxes when it comes to keeping urban environments in harmony with nature’s needs. (Image and video credit: Practical Engineering)

  • Kugel Fountains

    Kugel Fountains

    At science museums and tourist attractions around the world, visitors can spin the multi-tonne spheres of kugel fountains with the brush of their hand. The secret of the sphere’s mobility is aquaplaning – the same phenomenon that can cause cars to lose traction in wet conditions. In these fountains, the massive sphere sits in a precisely-shaped cup, with their surfaces separated by a thin layer of water. The entire system acts like a hydrostatic bearing, which allows the sphere to move freely. But even a relatively small disruption can destroy the effect, as happened to the Science Museum of Virginia’s original Grand Kugel after it cracked. (Image credit: E. Roberts; via Atlas Obscura; submitted by Kam-Yung Soh)

  • Rocking From The Waves

    Rocking From The Waves

    Not all seismic activity stems from earthquakes. In fact, much of Earth’s measured seismic waves come from interactions of the ocean and atmosphere with solid ground. Some of the strongest vibrations come from interactions of ocean waves, which transmit pressure waves that don’t attenuate with depth before passing into the solid Earth.

    How those waves propagate and scatter inside the Earth has been a matter of contention for decades, but recent simulations are beginning to uncover the mechanisms that lead to the waves seismologists measure. (Image credit: I. Mingazova; via Physics Today)

  • Following the Flow

    Following the Flow

    In early December 2020, the world’s largest iceberg — roughly 135 km long by 44 km wide — was heading straight for South Georgia Island. Luckily for the island, iceberg A-68A was being carried by ocean surface currents that approach the island before turning sharply southward. The enormous iceberg followed, rotating nearly 90 degrees and drifting away on faster currents.

    Scientists track these large-scale — 50 to 100 km wide — currents using satellites that measure the ocean height. Currents of this size actually generate a measurable tilt to the ocean surface, which scientists measure and use as input into models that estimate the surface currents’ speed and direction. (Image credit: L. Dauphin and J. Stevens; via NASA Earth Observatory)

  • Featured Video Play Icon

    Breaking Bubbles

    What do a nineteenth-century war ship, a sardine-hunting shark, and a viral bottle trick have in common? Cavitation! The phenomenon of cavitation occurs when a fluid is accelerated such that its local pressure drops below the vapor pressure. As a result, bubbles form and then violently collapse, creating shock waves that can damage nearby surfaces or stun prey. Dianna explains — and reveals some cool historical context that was new to me! — in the video above. (Image and video credit: Physics Girl)