Fluids Round-Up

Time for another fluids round-up! Here’s some of the best fluid dynamics from around the web:

- Band Ok Go filmed their latest music video in microgravity, complete with floating, splattering fluids. Here they describe how they did it. Rhett Allain also provides a write-up on the physics.

- Scientists are trying to measure the impact of airliners’ contrails on climate change. (pdf; via @KyungMSong)

- Researchers observing the strange moving hills on Pluto suspect they may, in fact, be icebergs.

- The best angle for skipping a rock is 20-degrees. Related: elastic spheres skip well even at higher angles. (via @JenLucPiquant)

- Fluid dynamics and acoustics have some fascinating overlaps. Be sure to check out “The World Through Sound” series at Acoustics Today, written by Andrew “Pi” Pyzdek, who also writes one of my favorite science blogs

- Over at the Toast, Mallory Ortberg explores the poetry of the Beaufort wind scale.

- Could dark matter be a superfluid? (via @JenLucPiquant)

- Understanding the physics of the perfect pancake is helping doctors treat glaucoma. (submitted by Maria-Isabel)

- Van Gogh’s “Starry Night” shows swirling skies, but just how turbulent are they? (submitted by @NathanMechEng)

- The physics (and fluid dynamics!) of throwing a football - what’s the best angle for a maximum distance throw? (submitted by @rjallain)

(Video credit: Ok Go)

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An old Black and white film about superfluids and thier strange properties, such as it’s frictionless fountains, abilitie to flow upwards and pass through solid objects. A fascinating look at how the truth can definitly be stranger than fiction.




Superfluidity is a state of matter in which viscosity of a fluid vanishes, while thermal conductivity becomes infinite. These unusual effects are observed when liquids, typically of helium-4 or helium-3, overcome friction in surface interaction at a stage (known as the “lambda point”, which is temperature and pressure, for helium-4) at which the liquid's viscosity becomes zero.

Superfluids, such as supercooled helium-4, exhibit many unusual properties. (See Helium#Helium II state). Superfluid acts as if it were a mixture of a normal component, with all the properties associated with normal fluid, and a superfluid component. The superfluid component has zero viscosity, zero entropy, and infinite thermal conductivity. (It is thus impossible to set up a temperature gradient in a superfluid, much as it is impossible to set up a voltage difference in a superconductor.) Application of heat to a spot in superfluid helium results in a wave of heat conduction at the relatively high velocity of 20 m/s, called second sound.

One of the most spectacular results of these properties is known as the thermomechanical or “fountain effect”. If a capillary tube is placed into a bath of superfluid helium and then heated, even by shining a light on it, the superfluid helium will flow up through the tube and out the top as a result of the Clausius-Clapeyron relation. A second unusual effect is that superfluid helium can form a layer, 30 nm thick, up the sides of any container in which it is placed. See Rollin film.

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