Not long ago, researchers showed that cats use friction to their advantage when drawing liquids into their mouths. New research shows that dogs rely on the same mechanism–they’re just far less efficient with it. The dog touches its backwards-curled tongue to the surface of the water; when it draws the tongue back, friction causes a column of fluid to follow. The dog then closes its jaws around the water. Some water also gets picked up by the back of the tongue, but since dogs have no cheeks, it spills out the sides, creating a mess familiar to dog owners. #
Tag: high-speed video
Gelatin
Gelatins are actually colloidal gels, or a liquid dispersed inside a solid, cross-linked network. The crosslinks give the gelatin structure, but much of its dynamic behavior remains reminiscent of fluid motion.
Giant Water Balloon Physics
Playing with a giant water balloon and high-speed cameras is like a giant experiment in surface tension, right up until the tensile strength of the balloon comes into play. The rippling in the balloon is reminiscent of the motion of droplet breakup or impact on superhydrophobic surfaces. (submitted by Daniel B)
Seeing Blast Waves
This clip shows high-speed video footage of a blackpowder explosion. As the blast wave expands, the surrounding air is heated, which changes its index of refraction. The strength of this change is great enough that we can distinguish the edges of the expanding shock wave by the visual distortion they cause to the view beyond the explosion.
Liquids Lens Breakup
A decane liquid lens floating on water (think drops of fat in chicken soup) displays different breakup and pinch-off than seen in three-dimensional droplet breakup. The pinch-off process in two dimensions relies on line tension rather than surface tension, and the quasi-2D liquid lens system is somewhere between these. The video above is a magnification of the filament connecting one liquid lens as it is broken into two smaller liquid lenses (the dark areas on the left and right of the screen). # (via scienceisbeauty)
Liquid Acrobatics
Imagine blowing through a straw into a nearly empty glass–we probably all did this as children and sent water, milk, and soda flying everywhere! In essence, this video shows that same act, but filmed by a high-speed camera. The “straw” blows a steady stream of helium into a shallow pool of silicone oil and slowly moves so that the angle the straw makes with the pool changes. As the angle changes, different regimes are visible. First waves appear on the surface of the pool, then a bulge forms, which develops into a droplet stream, then on into the chaos of bubbles and jets. It’s good I couldn’t see this in slow motion as a child or I would have never used my straw for drinking!
Underwater Explosions
As powerful as explosions can be above ground, they are even more dangerous underwater. Since water, unlike air, is incompressible, the pressure wave at the front of an underwater explosion is not damped to the extent it would be in air. A high-pressure, high-temperature bubble of gas also forms in the explosion, and, as with cavitation, if the bubble collapses near metal, the damage can be extensive. (via Gizmodo)
Droplet Impact on Superhydrophobic Surfaces
High-speed video of water droplets impacting on superhydrophobic surfaces demonstrates the impressive elasticity and surface tension of the droplets. Impacts vibrate and reflect through the droplet, but only a drop from the largest height actually causes breakup.
High-Speed Cooking
I suspect demonstrating fluid mechanics was not what this cookbook had in mind when they filmed creamer poured into coffee at 2000 fps, but there’s some awesome droplet breakup, crowning, roiling turbulent mixing, and even some deformed Worthington jets here. It’s a reminder that, even though we may not notice it, fluid dynamics are all around.
Dancing Droplets
When a droplet falls onto a larger pool of the same liquid, it briefly sits on a layer of air that prevents coalescence. When that air drains away, the coalescence cascade–in which the droplet breaks into progressively smaller droplets until fully absorbed–begins. But if you vibrate the pool of liquid, the droplet bounces, effectively injecting more air between it and the pool. This prevents coalescence. What’s really neat here is that the researchers demonstrate this effect with arrays of droplets dancing in formation.
