Earlier this week a Columbus, OH TV station tower camera caught this awesome timelapse footage of several microbursts in a thunderstorm. A microburst is a sudden, localized downdraft inside the storm. You can see a clear microburst starting at about 0:30 seconds. Note how it flares up and out as it hits the ground, eventually settling around the time a rainbow appears on the left edge of the frame. These strong winds moving down then curling out can be dangerous, both to structures on the ground and to any aircraft unfortunate enough to be taking off or landing in the storm. (Video credit: WCMH; submitted by
A. Bcstractor)
Videos
Microburst
Making Droplets Stick
Lots of plants have evolved leaves that are superhydrophobic – that is, water repellent. For a plant, this makes a lot of sense. A superhydrophobic leaf will make water bounce and run off, draining down to where the plants roots can drink it up. But this same feature can be a frustration to farmers who spread pesticides by spraying plants. They need the pesticide to stick to the leaves if it’s to deter insects, and the superhydrophobicity of the leaves forces them to spray more pesticides in the hopes of getting some to stick. Researchers at MIT are looking to change this status quo with a few biodegradable polymer additives that can counter the leaves’ superhydrophobic tendencies and help droplets stick to the surface. This could reduce the amount of pesticides needed to protect crops. (Video credit: MIT)
Quantum Droplets
Over the past decade, fluid dynamicists have been investigating tiny droplets bouncing on a vibrating fluid. This seemingly simple experiment has remarkable depth, including the ability to recreate quantum behaviors in a classical system. In this video, some of the researchers demonstrate their experimental techniques, including how they vary the frame rate relative to the bouncing of the drops. At the right frame rate, this sampling makes the droplets appear to glide along with their ripples, giving us a look at a system that is simultaneously a particle (drop) and wave (ripple). (Video credit: D. Harris et al.)
Rio 2016: Badminton
Badminton is unusual among racquet sports because it does not use a sphere as its projectile. Instead players hit a shuttlecock, traditionally made from a cork ball and a skirt of goose feathers. Despite its unusual shape, the shuttlecock reaches some of the fastest speeds in sports – over 330 kph (200 mph)! The shuttlecock’s high-drag form quickly slows shots down but also gives the game very different trajectories compared to other racquet sports.
It’s likely that, if you’ve played badminton yourself, you’ve played with a shuttlecock that has a plastic skirt rather than a feathered one. These synthetic shuttlecocks are cheaper and more durable, but they also have different drag characteristics than their feathered cousins. At low speeds, synthetic shuttlecocks have more drag than feathered ones, but at high speeds, the opposite is true. This is because the plastic skirt deforms more easily than the feathers, causing a synthetic shuttlecock’s skirt to collapse into a shape with less drag. (Video credit: Science Friday; research credit: F. Alam et al.)
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Starting a Lighter
Lots of fluids are transparent, which makes it hard for us to appreciate their motion. One technique for making these invisible motions visible is schlieren photography, which makes differences in density visible. Here it’s combined with high-speed video to show what happens when you use a lighter (minus the spark!). When the fuel starts flowing, it’s unstable and turbulent, but after that initial start-up, you can see the jet settle into a smooth and laminar flow. Wisps of fuel diffuse away from the jet as the fluid disperses. As the valve shuts off, the flow becomes unstable again, and the remains of the lighter fluid diffuse away. (Video credit: The Missing Detail)
Crash Course Fluids
Crash Course Physics returns to the subject of fluids with their video on fluid dynamics. They stick with ideal fluids (i.e. incompressible, inviscid, laminar flows) for simplicity and cover some of the basics by discussing conservation of mass (also called continuity) and a simple form of Bernoulli’s equation. Despite keeping things basic, the video does a nice job introducing these topics; I especially like that they explain Bernoulli’s equation as a form of conservation of energy. Sometimes it’s easy to let the terminology in fluid dynamics mask the fact that the equations we use are just alternative forms of the classical equations for conserving mass, momentum, and energy. As with their fluids at rest video, the information is densely packed, so expect to pause and rewind. (Video credit: Crash Course)
“Vorticity”
Photographer Mike Olbinski is back with another storm-chasing timelapse entitled “Vorticity”. Like his previous work, this film is a breath-taking example of physics in action. It is well worth taking a few minutes to watch in fullscreen, at high resolution, and with headphones. Olbinski’s timelapses beautifully capture the incredible dynamic motion of our atmosphere. Fittingly, “Vorticity” is all about the swirling, roiling motion of supercell thunderstorms and the tornadoes they can spawn, but the film also captures many other great phenomena from the convection that builds clouds to unusual formations like undulatus asperatus and mammatus clouds. (Video credit: M. Olbinski; submitted by Paul vdB)
Crash Course Hydrostatics
Crash Course Physics has just put out an episode on fluids at rest (a.k.a. hydrostatics). For those who are unfamiliar, Crash Course is an educational YouTube channel that offers fun, instructional videos on a large and ever-growing array of topics. In this video, they tackle a lot of important basics for fluids, including the principles behind hydraulics, how to measure pressure, and how buoyancy works. It’s pretty densely packed, and, if you’re learning the concepts for the first time, you’ll probably pause and rewatch some segments, but even if you’re familiar with the topics, it’s a nice refresher. (Video credit: Crash Course Physics)
“Memories of Paintings”
In “Memories of Paintings,” Thomas Blanchard gives us an up-close view of fluids and mixing. It’s a calming and curious video made from combinations of paint, oil, oat milk, and soap. The fluids feather and intertwine, driven by differences in surface tension. Paint gets encapsulated by immiscible oil to create little islands of color that float and dance against the background. It’s a fun journey through effects that we witness daily but rarely take the time to watch. (Video credit: T. Blanchard; via Gizmodo)
Flamethrowing
Humans have long been fascinated by staring into flames, and the Slow Mo Guys carry on the grand tradition here with 4K, high-speed video of a flamethrower. Like firebreathers, a flamethrower’s fire is the result of a spray of tiny, volatile droplets of fuel. Once ignited, the spray becomes a turbulent jet of flames. Turbulent flows are known for having both large and small-scale structure, and there’s some really great close-ups showing this around the 2:00 mark. Also watch the edges of the flame, where the nearby air has gotten hot enough to shimmer. You can see how the trees in the background ripple and blur as the fire heats up the air and changes its density and refractive index. (Video credit: The Slow Mo Guys)