Ever notice the distinctive ring that forms in your kitchen sink when you turn the water on? This phenomenon is known as a hydraulic jump; it occurs when a fast moving fluid (the water just discharged from the faucet) runs into a slow moving fluid (the water that’s been sitting in the sink) and transfers some of its kinetic energy into potential energy by increasing its elevation. Researchers have recently shown that this everyday occurrence is actually a physical analog to a white hole, the cosmological inverse of a black hole. (In theory, a white hole cannot be entered, but light and matter can escape it.) Check out Wired’s article for an explanation of the clever experiment that showed the equivalence of the two. #
Tag: jets
Breaking up in Crossflow
This video shows some instabilities that occur when a liquid jet impinges on a flowing cross stream. Note how the jet breaks down into droplets in a fashion similar to the Plateau-Rayleigh instability but the broken tip remains stable for some time thereafter. #
Whipping Instabilities
When jets of liquid are introduced into an electrified medium in a process known as electrospinning, they can exhibit behavior known as whipping instabilities.
Dripping into Droplets
The Plateau-Rayleigh instability is one that just about everyone has witnessed. It describes how a liquid jet breaks up into droplets. Notice the waviness in the jet before breakdown. The tiniest curvature in the jet causes an imbalance in the liquid’s pressure due to surface tension. Because the system is unstable, any small changes will become larger, ultimately resulting in the jet breaking into droplets.
Can a Squid Fly?
Evidence is mounting that several kinds of squid will use jets of water to propel themselves into the air where they can actively fly some 50 times their body length.
