This high-speed footage shows how a dog drinks. The dog’s tongue curls backwards, creating a large area of surface contact with the water. When the dog pulls its tongue back up, water adheres to it and is drawn upward in a column. The dog then closes its mouth around the water before it falls. Fundamentally, this is the same mechanism as the one cats use. Part of the reason that dogs are messier drinkers, though, is that the backwards curl of their tongue picks up extra water. Because the dog has no cheeks, there’s no way to move this water from the underside to the top of the tongue and so the water just falls back out. (Video credit: Oxford Scientific Films; submitted by Carolyn W.)
Search results for: “high-speed video”
Hydrophobia
On a recent trip to G.E., the Slow Mo Guys used their high-speed camera to capture some great footage of dyed water on a superhydrophobic surface. Upon impact, the water streams spread outward, flat except for a crownlike rim around the edges. Then, because air trapped between the liquid and the superhydrophobic solid prevents the liquid from wetting the surface, surface tension pulls the water back together. If this were a droplet rather than a stream, it would rebound off the surface at this point. Instead, the jet breaks up into droplets that scatter and skitter across the surface. There’s footage of smaller droplets bouncing and rebounding, too. Superhydrophobic surfaces aren’t the only way to generate this behavior, though; the same rebounding is found for very hot substrates due to the Leidenfrost effect and very cold substrates due to sublimation. As a bonus, the video includes ferrofluids at high-speed, too. (Video credit: The Slow Mo Guys/G.E.)
Holiday Fluids
BYU Splash Lab–those breakers of bottles, skippers of rocks, spinners of eggs, students of soap films, masters of splashes, and all-around cool fluid dynamicists–have some fluids-themed, high-speed holiday greetings. Likewike, here at FYFD we’ll be spending the next week celebrating the physics and fluid dynamics of the winter holiday season! In the meantime, you can whet your appetite by brushing up on your cookie dunking techniques, watching how icicles form, and enjoying a good beverage. Stay tuned and happy holidays from FYFD! (Video credit: BYU Splash Lab/BYU News)
Bullet Through a Bubble
A bullet passes through a soap bubble in the schlieren photo above. The schlieren optical technique is sensitive to changes in the refractive index and, since a fluid’s refractive index changes with density, permits the visualization of shock waves. A strong curved bow shock is visible in front of the bullet as well as weaker lines marking additional shocks waves around the bullet. Impressively, the bullet’s passage is so fast (and the photo’s timing so perfect) that there are no imperfections or signs of bursting in the soap bubble. The photo’s caption suggests that the bubble may be filled with multiple gases. If they are unmixed and of differing densities, this may be the source of the speckling and plume-like structures inside the bubble. Incidentally, if anyone out there has high-speed schlieren video of a bullet passing through a soap bubble, I would love to see it. (Photo credit: H. Edgerton and K. Vandiver)
Put the Lid Down When You Flush
Hospital-acquired infections are a serious health problem. One potential source of contamination is through the spread of pathogen-bearing droplets emanating from toilet flushes. The video above includes high-speed flow visualization of the large and small droplets that get atomized during the flush of a standard hospital toilet. Both are problematic for the spread of pathogens; the large droplets settle quickly and contaminate nearby surfaces, but the small droplets can remain suspended in the air for an hour or more. Even more distressing is the finding that conventional cleaning products lower surface tension within the toilet, aggravating the problem by allowing even more small droplets to escape. To learn more, see the Bourouiba research group’s website. (Video credit: Bourouiba research group)
“Supermajor”
In Matt Kenyon’s “Supermajor,” oil appears to flow upward against gravity from a puddle into a can. This optical illusion is a stroboscopic effect similar to the one that makes car wheels seem to rotate backwards. The human eye and brain can be tricked into seeing the stream of oil as being suspended or even moving backwards by changing the flicker of the lighting relative to the rate at which the drops fall. If you watch the videos carefully, the pedestal is vibrating, which imparts a specific frequency to the falling drops. Combine this with a light that flickers at a slightly different frequency than that of the vibration and you can make the stream of drops appear to move up or down. It’s a helpful way to trick the brain into freezing fluid motion we would normally be unable to appreciate without high-speed cameras. (Video credit: Science Gallery; exhibit credit: Matt Kenyon; submitted by jshoer)
Flame Feedback
When a flame is enclosed in a combustion chamber, it can create violent oscillations in the pressure field. Flames have a natural unsteadiness in their heat release. These temperature fluctuations create pressure waves in the chamber. In the right enclosure, those pressure waves resonate and feed energy back into the initial perturbation. This creates a self-exciting oscillation, not dissimilar from aeroelastic flutter. This combustion instability is known as a thermoacoustic instability because of the coupling between temperature and pressure (acoustic) waves. The quick demo above lets you see and hear such an instability; here’s the same setup in high-speed, which makes the oscillating flame even clearer. The violence of this instability can be great enough to destroy engines. Famously, the F1 engine used in the Saturn V rocket had a history of instability issues before the fuel-injector was redesigned. For another great demo of this effect, check out this video from T. Poinsot. (Video credit: V. Anandan)
Falcon vs. Raven
Earth Unplugged has posted some great high-speed footage of a peregrine falcon and a raven in flight. Notice how both birds draw their wings inward and back on the upstroke. By doing so, they decrease their drag and thus the energy necessary for flapping. On the downstroke, they extend their wings fully and increase their angle of attack, creating not only lift but thrust. The falcon boasts an incredibly streamlined shape, not only along its body but also along its wings. In contrast, the raven has broader wings with large primary feathers that fan out near the tips. Splaying these large feathers out decreases the strength of the bird’s wingtip vortices, thereby reducing downwash and increasing lift, much the same way winglets do on planes. That extra lift and control the big primaries provide is important for the raven’s acrobatic skill. (Video credit: Earth Unplugged; via io9)
Fire-Breathing Physics
One of the most dangerous stunts for any fire-eater is breathing fire. Dr. Tim Cockerill explains some of the science behind the feat in this video. Volatility–the tendency of the liquid fuel to vaporize–is actually the enemy of a fire-eater. Use a fuel that is too volatile and it will catch fire too easily when the vaporous fuel mixes with the air. Instead fire-eaters use less volatile fuels and spray a mist of fine droplets to mix the air and fuel. This atomization of the fuel creates a spectacular fireball without endangering the fire-eater (as much). To see a similar fireball in high-speed, check out this post. (Video credit: T. Cockerill/The Ri Channel; via io9)
Bouncing on a Pool
There’s something wonderfully serene about watching water droplets skate their way across the surface of a pool. Here the pool of water is being vibrated at a frequency just below the Faraday instability – meaning that no standing waves form on the surface. Instead, the bounce is just enough to create a thin layer of air between the droplet and the pool to prevent coalescence. With each bounce, gravity’s effect on the water tries to drain the air away, but each rebound lets more air rush in to hold the droplet up. Eventually, gravity wins and the droplets coalesce into the pool. In high-speed that process is mesmerizing, too. (Video credit: K. Welch)