Tag: physics

Freezing Soap Bubbles
I’m not a winter person, but there’s something almost magical about the way water freezes. From instant snow to snow rollers and weird ice formations to slushy waves, winter brings all kinds of bizarre and unexpected sights. The video above is an artistic look at one of my favorites – freezing soap bubbles. Normally, the thin film of a soap bubble is in wild motion, convecting due to gravity, surface tension differences, and the surrounding air. Such a thin layer of liquid loses its heat quickly, though, and, as ice crystals form, the bubble’s convection and rotation slow dramatically, often breaking the thin membrane. Happily photographer Paweł Załuska had the patience to capture the beautiful ones that didn’t break! (Video credit: P. Załuska; via Gizmodo)
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February 11, 2016
The Leidenfrost Dunk
The Leidenfrost effect occurs when a liquid is exposed to a surface so hot that it instantly vaporizes part of the liquid. It’s typically seen with a drop of water on a very hot pan; the drop will slide around, nearly frictionless, upon a cushion of its own vapor. You can see the effect when plunging a hot object into a bath of liquid, too. This is what happens when you quickly dunk a hand in liquid nitrogen (not recommended, incidentally) or when you drop a red hot steel ball into water like above. In this case, the object is so hot that it gets encased in a layer of water vapor. If you could maintain the temperature difference necessary to keep the vapor layer intact, you could move underwater at high speeds with low drag, similar to the effects of supercavitation. (Image credit: Paul Pyro, source)
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February 10, 2016
Tears of Wine
Give your wine glass a swirl and afterward you may notice little rivulets of wine along the side of your glass. These so-called “tears of wine” or “wine legs” are caused by a combination of evaporation, surface tension, and gravity. After the glass has been swirled, alcohol from the thin layer of wine on the glass wall quickly evaporates, leaving behind a fluid that is more watery than the wine in the glass. Since water has a higher surface tension than alcohol or wine, it pulls more fluid up the wall via the Marangoni effect. This carries on until enough wine is pulled up to form a droplet that’s heavy enough to slide down the glass. This up-and-down exchange of fluid is nicely illustrated in the video above, where the tiny particles in the wine help show how flow gets drawn up even as your eye follows the drops sliding down. (Video credit: A. Athanassiadis and K. Khalil; submitted by Thanasi A.)
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February 9, 2016
Phytoplankton Flows
Phytoplankton, tiny plant-like organisms that live in ocean waters, act like nature’s tracer particles, making visible flows that would otherwise go unnoticed. In this satellite imagery, a phytoplankton bloom in the Southern Ocean off the coast of Antarctica highlights the turbulence of this region. Strong, steady winds and currents are typical for this area, which helps drive heat exchange between the ocean and atmosphere. The swirling eddies we see – many of them 100 km across! – are evidence of that turbulence. They’re also a sign of nitrogen and other nutrients getting mixed up in the action; it’s these nutrients that help generate the bloom in the first place. (Image credit: N. Kuring/NASA Earth Observatory)
February 8, 2016
Skipping Squishy Spheres
Skipping a stone on water requires a flat, disk-like stone thrown at a shallow angle, but elastic spheres are remarkable skippers, too, even at higher impact angles. Researchers at the Splash Lab have just published their work on why these balls skip so well. As seen in the top animation, the elastic spheres deform on impact, flattening to a more disk-like shape that rides at an angle of attack relative to the air-water interface. Both features are important to the spheres’ enhanced skipping. By flattening, the sphere comes into greater contact with the water and by orienting at a larger angle of attack, the sphere increases the vertical component of force the water generates on the sphere. It’s this vertical force that lifts the sphere up and lets it keep bouncing.
Because the ball is soft, it keeps deforming after its impact and bounce (see top animation). For some skips, the timescale of the sphere’s elastic waves is smaller than the length of time the sphere is in contact with the water. When this is the case, the sphere’s elastic waves will affect the impact cavity in the water, forming what the researchers call a
matryoshka cavity, after the Russian nesting dolls. An example is shown in the second animation. For more, check out the USU press release, the original paper, or the award-winning video they made a few years ago. (Image credits: J. Belden et al./The Splash Lab)
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February 5, 2016
Fluids Round-up
Here’s to another fluids round-up, our look at some of the interesting fluids-related stories around the web:
– Above is a music video by Roman Hill that relies on mixing and merging different fluids and perturbing ferrofluids for its visuals as it re-imagines the genesis of life.
– GoPro takes viewers inside a Category 5 typhoon with 112 mph (180 kph; 50 m/s) winds.
– Astronaut Scott Kelly demonstrates playing ping pong with a ball of water in space. (via Gizmodo)
– See fluid dynamics on a global scale with Glittering Blue. (via The Atlantic)
– To make a taller siphon, you have to find a way to avoid cavitation.
– Speaking of siphons, Randall Munroe tackles the question of siphoning water from Europa over at What If? (submitted by jshoer)
– The Mythbusters make a giant tanker implode using air pressure.
– Sixty Symbols explores how tiny things swim.
– What happens when you bathe in 500 pounds of putty? Let’s just say that bathing in an extremely viscous non-Newtonian fluid is not recommended. (via Gizmodo)
(Video credit and submission: R. Hill et al.)
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February 4, 2016
Ode to Bubbles
Boiling water plays a major role in the steam cycles we use to generate power. One of the challenges in these systems is that it’s hard to control the rate of bubble formation when boiling. In this video, researchers demonstrate their new method for bubble control in a clever and amusing fashion. The twin keys to their success are surfactants and electricity. Surfactant molecules, like soap, have both a polar (hydrophilic) end and a non-polar (hydrophobic) end. By applying an electric field at the metal surface, the researchers can attract or repel surfactant molecules from the wall, making it either hydrophobic or hydrophilic depending on the field’s polarity. Since hydrophobic surfaces have a high rate of bubble formation, this lets the scientists essentially turn nucleation on and off with the flip of a switch! (Video credit: MIT Device Research Lab; see also: research paper, MIT News Video, press release)
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February 3, 2016
Pancake Ice in the Sea
Sea ice forms in patterns that depend on local ocean conditions. Pancake ice, like that shown in the above photo from the Antarctic Ross Sea, is formed in rough ocean conditions. Each individual pancake has a raised ridge along its edge, due to wave-induced collisions with other pieces of ice. Over time the smaller pieces of ice will merge together, forming large sheets. Evidence of its turbulent formation will persist, however, in the rough surface of the ice’s underside. For more, check out the National Snow and Ice Data Center. (Image credit: S. Edmonds; via Flow Visualization)
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Reminder: If you’re at the University of Illinois at Urbana-Champaign, I’m giving a seminar this afternoon. Not in Illinois? I’ve got other events coming up, too!
February 2, 2016
Wave Clouds
In this video, Sixty Symbols tackles the physics of wave clouds. When air flows over an obstacle like a mountain, the air can begin to oscillate downstream, forming what is known as a lee wave. As the air bobs up and down, it will cool or warm according to its altitude. At cooler conditions, if the air is moist, it can condense into a cloud at the peak of its oscillation. If you observe this behavior over time, you get what appear to be regularly-spaced stripes of clouds. This is actually a pretty common phenomenon to see, depending on where you live. It’s an example of internal waves in the atmosphere. (Video credit: Sixty Symbols)
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Reminder: If you’re at the University of Illinois at Urbana-Champaign, I’m giving a seminar tomorrow afternoon. Not in Illinois? I’ve got other events coming up, too!
February 1, 2016
Pouring Molten Aluminum on Dry Ice
What happens when you pour molten aluminum on dry ice? As the Backyard Scientist shows, you get what looks like slippery, sliding, boiling metal. In fact, what you see may remind you of the Leidenfrost effect, where a liquid can slide around over an extremely hot surface on a thin film of its own vapor. Despite the opposite temperature extremes–this is a very cold surface rather than a very hot one–a very similar thing is happening here. The molten aluminum is so much hotter than the dry ice that it causes the dry ice to sublimate, releasing gaseous carbon dioxide that the aluminum slides around on. For the same reason, the aluminum appears to boil in the bottom animation. What we’re really seeing is carbon dioxide gas rising and escaping the aluminum so violently that it carries some of the metal with it. Be sure to check out the full video for more awesome physics! (Image credit: The Backyard Scientist, source; via Gizmodo)
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January 29, 2016