But if we stir a superfluid, the tornado will continue forever even once the spoon has been removed. For example, if we stir a cup of tea and create a 'tornado', as soon as we remove the spoon the tornado starts to slow down and eventually stops. “It changed everything we thought we knew about the laws of friction. “This unimpeded flow was one of the most exciting properties of a superfluid,” explains Dr Nick Parker, Senior Lecturer in Applied Mathematics and co-author on the paper. Along with other properties, these became the ‘hallmarks of superfluidity’. It would be several decades later, however, before scientists were able to explain the strange properties of the super-cold helium - its lack of viscosity and its constraint to swirl only through tiny tornadoes of fixed size and strength. In 1908, Dutch physicist Kamerlingh Onnes became the first person to liquefy helium and two years later he discovered the when it was cooled to just a couple of degrees above absolute zero, it would abruptly stop boiling. Helium is one of the few known elements that will never become a solid but remains a liquid even at extremely low temperatures. One of the most important discoveries of the 20th century “This means that, contrary to our past understanding, superfluid helium actually behaves in much the same way as an ordinary fluid.” Data at other public NIST sites: NIST Atomic Spectra Database - Lines Holdings (on physics web site) NIST Atomic.
It lets you create a web page that adapts to three browser widths: one for a. “So in our teacup, what we would actually see around the edge is a ‘storm’ – a layer of whirling tornadoes sticking together and bringing the flow of fluid closest to the boundary almost to a halt. mm nearly every type of web - XSLIII'nQmeIIIJ Helium III'IuaH. “These swirling vortices tangle together like spaghetti and - just like when you drain your spaghetti and leave it for too long in a pan – they stick together, creating a slow-moving boundary layer between the free-moving fluid and the surface. If the surface is ‘rough’ down to the scale of nanometres, as all surfaces are, then mini tornadoes are created as the superfluid flows past the surface. “What our research has shown is that this phenomenon is only true for perfectly smooth surfaces. “Or at least this is what has always been believed. “But if we were to repeat with a cup of superfluid helium, the fluid would keep swirling forever since there is no friction, and no boundary layer, to hold it back. This “boundary layer” soon causes the flow to grind to a halt. Due to friction, adjacent layers of fluid get held back as they try to swirl around the cup.
“It looks like the whole of the tea is swirling, but actually at the wall of the cup the tea stands still since it gets stuck there. “Imagine you stir a cup of tea and then remove the spoon,” he explains. Lead author on the paper Dr George Stagg, from the School of Mathematics & Statistics at Newcastle University, says that to visualise the research findings you only need to think of your morning cuppa.
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