Life is just a theory

fuckyeahfluiddynamics:

A drop of red dye falls into a thin layer of milk, forming a crown splash. Notice the pale edges of the droplets at the rim of the crown; this is milk that has been entrained by the original drop. The rim and satellite droplets surrounding the splash are formed due to surface tension effects, chiefly the Plateau-Rayleigh instability—the same effect responsible for breaking a falling column of liquid into droplets like in a leaking faucet. The instability will have a most unstable wavelength that determines the number of satellite droplets formed. (Photo credit: W. van Hoeve et al., University of Twente)

fuckyeahfluiddynamics:

Differences in surface tension between two layers of fluid can cause fascinating finger-like instabilities.  Here glycerol is spread in a thin film on a silicon wafer.  Then a wire coated in oleic acid, which has a lower surface tension than glycerol, was touched to the wafer.  As the oleic acid spreads across the film surface, Marangoni and capillary stresses cause variations in the film thickness, which results in the dendritic patterns seen here. (Photo credit: B. Fischer et al.)

These time-lapsed images capture what happens above and below the surface when a water droplet falls into a pool of water. Check out the vortex below the surface! The droplet is dyed blue to make it easier to see. (Slow-motion videos can also provide a cool visual.)

The process seen here, called a droplet coalescence, occurs because the surface of the larger body of water has been coated in water-repelling oil. At first, the oil on the surface keeps the droplet afloat, but eventually a tiny hole forms in the oil layer, and capillary action sucks the water droplet into the larger body of water. But as its shape deforms to fit into that hole, the droplet pinches off a daughter droplet, which flies into the air and then falls back to land on the surface once more. And then the whole thing starts all over again.

But this particular image comes from a paper in Physical Review Letters. In this study, researchers from UC-Davis did more than take pictures. They managed to control the size of the daughter droplet by giving the water droplets an electrical charge, and then varying an external electrical field. It turns out that capillary action isn’t the only force in play during a droplet coalescence. The behavior of charged droplets also depends on electrostatic interactions between the droplets and the larger body of liquid.

jtotheizzoe:

Superhydrophobic carbon nanotube water droplet bouncing GIF goodness. 

(From this post)

Nnnng is there anything more awesome than fluid dynamics? No. Nothing more awesome.

quantumaniac:

Cheerios Effect

In fluid mechanics, the study of fluids and their reaction to forces, the Cheerios effect is the observable tendency for small floating objects to attract one another.  It is obviously named for Cheerios, the breakfast cereal - because the small o’s tend to clump together or cling to the sides of the bowl. The effect is caused by surface tension and buoyancy, and the effect also acts towards the behavior of bubbles in soft drinks to stick together. 

The effect applies to any small, yet macroscopic object that floats or clings to the surface of a liquid. Some liquids, notably water, when near the side of a glass form a meniscus - a curved section of the liquid. 

When these small objects are placed in the liquid, they form a dent in the formerly smooth surface. If two objects placed in the same liquid are close enough together, they will ‘fall in’ to each other because of these small dents. Additionally, objects near the edge of the bowl interact with the meniscus and curve upwards along it - appearing to cling to the side. Thus, there is no attractive force between the objects, but rather the effect is due to the geometry of the liquid surface.