Celebrating the physics of all that flows with Nicole Sharp, Ph.D.
- Profile
Viscous Fingers
The Saffman-Taylor instability occurs when a less viscous fluid is injected into a more viscous one, usually in a Hele-Shaw cell. Here oil paint and mineral spirits were painted onto flat surfaces that were pressed together before being pulled apart. The result is viscous fingering of the fluids. #
How Dogs Drink
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…
Volcanic Ash Plume
Video footage of Iceland’s Grimsvotn volcano erupting shows a massive turbulent plume of ash. The largest scales of the plume are of the order of hundreds, if not thousands of meters, and the eddies of the plume appear to move very slowly, especially far from the base. According to Kolmogorov, however, at the smallest scales…
Flowing Up a Waterfall
Tea-drinking physicists found that it’s possible for particles to flow up a short (< 1 cm) waterfall to contaminate pure upstream sources. Their apparatus is shown above, along with an inset showing the velocity field on the surface of the channel. The blue arrows indicate flow downstream and the red arrows indicate counterflow that carries…
Ferrofluid Self-Organization
The behavior of a ferrofluid subject to magnetic fields can be fascinating. Here a ferrofluid is subjected to a permanent magnet and thinner is added to the ferrofluid. As it spreads outward, the thinner carries ferrofluid with it. The thinner evaporates, increasing the concentration of ferrofluid in the outer ring and eventually forming peaks of…
Feathering on SpaceShipTwo
Virgin Galactic and Scaled Composites recently performed their first feathered flight with SpaceShipTwo, which is on track to be the first commercial spaceship. Feathering is a re-entry technique devised by Scaled Composites founder Burt Rutan: Once out of the atmosphere the entire tail structure of the spaceship can be rotated upwards to about 65º. The…
White Hole Analogues
A white hole–the cosmological opposite of a black hole–is a singularity from which matter emerges but which matter can never enter from beyond the event horizon. Hydraulic jumps, those rings that sometimes appear in the kitchen sink, turn out to be a physical analog of this behavior. The photo above shows a hydraulic jump with…
Venom Properties
Most venomous snakes deliver venom to their prey via grooves in their fangs, rather than through a pressurized bolus through hollow fangs. New research shows that these venoms are shear-thinning non-Newtonian fluids. The surface tension of the venom is such that a drop of venom will tend to flow into and down the groove. Once…
Airplane Vortex Wake
The wingtip vortices in the wake of a commercial airliner distort the clouds as the plane descends. Wingtip vortices form as a result of high pressure air from the underside of the wing accelerating around the wingtips to reach the low pressure on top of the wing. They can be hazardous to other (lighter) aircraft.…
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.