FYFD

Category: Phenomena

  • Auroras

    Auroras

    Beautiful auroras are the result of ions in the solar wind exciting atoms in our atmosphere. This example of magnetohydrodynamics is typically only visible in the far northern and southern reaches of the globe. But in recent years, citizen scientists noticed a new aurora outside the polar regions. It looked like a narrow purple streak with occasional fingers of green. It got nicknamed Steve. Recent satellite measurements show that the aurora seems to be a visible emission from a known phenomenon, subauroral ion drift, which features a rapid flow of charged ions. In Steve’s case, this flow moves nearly 6 km/s and is around 6000 degrees Celsius. Scientists have dubbed the aurora S.T.E.V.E., Strong Thermal Emission Velocity Enhancement, to honor the original nickname. Learn more from NASA and Science magazine. (Image credit: K. Trinder; NASA GSFC/CIL/K. Kim, source)

  • Cloud Chambers

    Cloud Chambers

    Cloud chambers were one of the first methods used to study radioactive decay and cosmic particles. Such chambers are filled with a cool, supersaturated cloud of alcohol vapor. When high-energy particles pass through, they collide with atoms in the chamber, ionizing them. Those ions then serve as nucleation sites for the alcohol vapor, creating a condensation streak that marks the particle’s passage. In some respects, they’re similar to the contrails that form behind airplanes. What you’re seeing is not the particle itself but evidence that it went by. YouTuber Nick Moore built his own cloud chamber. Learn more about it and see lots more great footage of it in action in the full video below. (Image and video credit: N. Moore)

  • Visualizing Acoustic Levitation

    Visualizing Acoustic Levitation

    The schlieren photographic technique is often used to visualize shock waves and other strong but invisible flows. But a sensitive set-up can show much weaker changes in density and pressure. Here, schlieren is used to show the standing sound wave used in ultrasonic levitation. By placing the glass plate at precisely the right distance relative to a speaker, you can reflect the sound wave back on itself in a standing wave, seen here as light and dark bands. The light bands mark the high-pressure nodes, where the pressure generated by the sound waves is large enough to counteract the force of gravity on small styrofoam balls. This allows them to levitate but only in the thin bands seen in the schlieren. Move the plate and the standing wave will be disrupted, causing the bands to fade out and the balls to fall. (Video and image credit: Harvard Natural Sciences Lecture Demonstrations)

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    Paint Balloons

    The Slow Mo Guys have a history of personal sacrifice in the name of cool high-speed footage, and their Super Slow Show is no exception. In a recent segment, both Dan and Gav were knocked flat by giant swinging balloons of paint, and, as you might expect, the splashes are spectacular. The speed is just right for some of the paint to form nice sheets before momentum pulls them into long ligaments. Eventually, that momentum overcomes surface tension’s ability to keep the paint together, and the paint separates into droplets, which, as you see below, rain down on the hapless victims. (Video and image credit: The Slow Mo Guys)

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    Under Pressure, Part 2

    Our adventures with pressure continue after the trip to the aquarium. To see just how much pressure we could generate with height, A.J. and I teamed up with the Corvallis Fire Department to recreate an experiment attributed to 17th-century French physicist Blaise Pascal. In Pascal’s experiment, he (supposedly) used a column of water to burst a wooden barrel. In ours, we use a ladder truck to make a 30-meter column of water burst a glass carboy! We also got a little help from our friends at the Lutetium Project to introduce you to Pascal and his work. (Thanks, Guillaume!) We’ll tell you more about Pascal and his contributions in an upcoming video, so stay tuned. (Video and image credit: A. Fillo and N. Sharp)

  • Space Shuttle Sonic Booms

    Space Shuttle Sonic Booms

    The Space Shuttle had a famous double sonic boom when passing overhead during re-entry. This schlieren flow visualization of a model shuttle at Mach 3 reveals the source of the sound: the fore and aft shock waves on the vehicle. The nose of the shuttle generates the strongest shock wave since it is the first part of the vehicle the flow interacts with. This initial shock wave turns the flow outward and around the shuttle. The second boom comes from the back of the shuttle and serves to turn the flow back in to fill the wake behind the shuttle. (The actual shock wave would look a little different than this one because there’s no sting holding the shuttle like there is with the model.) The other major shock wave comes from the shuttle’s wings, but, at least for this Mach number, the wing shock wave merges with the bow shock, making the two indistinguishable. (Image credit: G. Settles, source)

  • Rain on Car Windows

    Rain on Car Windows

    As a child, I loved to ride in the car while it was raining. The raindrops on the window slid around in ways that fascinated and confused me. The idea that the raindrops ran up the window when the car moved made sense if the wind was pushing them, but why didn’t they just fly off instantly? I could not understand why they moved so slowly. I did not know it at the time, but this was my early introduction to boundary layers, the area of flow near a wall. Here, friction is a major force, causing the flow velocity to be zero at the wall and much faster – in this case roughly equal to the car’s speed – just a few millimeters away. This pushes different parts of large droplets unevenly. Notice how the thicker parts of the droplets move faster and more unsteadily than those right on the window. This is because the wind speed felt by the taller parts of the droplet is larger. Gravity and the water’s willingness to stick to the window surface help oppose the push of the wind, but at least with large drops at highway speeds, the wind’s force eventually wins out. (Image credit: A. Davidhazy, source; via Flow Viz)

  • Caught in a Whirl

    Vortex rings may look relatively calm, but they are concentrated regions of intensely spinning flow, as this poor jellyfish demonstrates. The rings form when a high-speed fluid gets pushed suddenly (and briefly) into a slower fluid. In the case of this bubble ring, a burst of air is pushed by a diver into relatively still water. The vorticity caused by the two areas of fluid trying to move past one another forms the ring. Like a spinning ice skater who pulls his arms inward, the narrow core of the vortex spins fast due to the conservation of angular momentum. Meanwhile, the bubble ring moves upward due to its buoyancy, pulling nearby water in as it goes. This catches the hapless jellyfish (who relies on vortex rings itself) and gives it quite a spin. But. don’t worry, the photographer confirmed that the jelly was okay after its ride. (Video credit: V. de Valles; via Ashlyn N.)

  • Castle-like Clouds

    Castle-like Clouds

    An astronaut captured this towering cloud over Andros Island from orbit aboard the ISS. This is a cumulus castellanus cloud, named for the castle-like crenelations at its top. Castellanus clouds form in areas with strong vertical updrafts, often due to cloud-level atmospheric instabilities rather than heating at the Earth’s surface. These clouds frequently proceed rain or even thunderstorms. What distinguishes castellanus from other types of cumulonimbus clouds is their shape: castellanus clouds have protrusions that are taller than they are wide – like the castles for which they are named. (Image credit: NASA / Expedition 48; via NASA Earth Observatory)

  • When Friction Isn’t Enough

    When Friction Isn’t Enough

    If you try to build a pyramid of dry glass beads, you’ll have a hard time of it. The frictional forces simply aren’t enough to hold the beads together against the force of gravity. If you add a little water, though, the story is different. The intermolecular forces inside water give it a lot of cohesion, which helps it fill the narrow gaps between beads. That added capillary force gives just enough additional sticking power to hold a pyramid of beads together. (Image and video credit: amàco et al.)