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Asked by ebygum to Adam, Geoff, Rob, Sheila, Suzie on 18 Mar 2011 in Categories: General.
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Adam Tuff answered on 18 Mar 2011:
I am by no means an expert on superfluids, but fluids that display properties of bose-einstein condensates don’t conform to the rules of normal fluids. At extremely low temperatures the atoms in the fluid all have the same quantum state – if one moves, they all move! This means they can do weird things like creep up walls of containers and have amazing properties like incredibly high thermal conductivity.
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Suzie Sheehy answered on 18 Mar 2011:
Superfluidity is a different state of matter, which happens to helium when you cool it down (as you say) to almost absolute zero. I don’t know why it becomes superfluid but I suspect it has to do with quantum mechanics on that level!
(I could look it up on google but I don’t think that’s the point of these questions…) -
Sheila Kanani answered on 18 Mar 2011:
Great questions, I love superfluids they look like stuff out of movies!
Researchers have known for decades that if you cool liquid helium just a few degrees below its boiling point of about –269 degrees C it will suddenly be able to do things that other fluids can’t, like climb up and over the sides of a dish, and remain motionless when its container is spun. No longer a mere liquid, the helium has become a superfluid, this is basically a liquid that flows without friction. Superfluidity comes from the weird rules of quantum mechanics.
The reason this happens to helium is helium’s unique ability to remain liquid down to absolute zero. When most liquids are cooled, the slight attraction between atoms in the fluid begins to overcome heat vibrations, and the particles settle into a regular order, namely a solid. But helium atoms are so light and weakly drawn to one another that the atoms jiggle and they never settle into the solid state.
Helium’s liquidity at low temperatures allows it to carry out a transformation called Bose–Einstein condensation, in which individual particles overlap until they behave like one big particle. Atoms acting in unison don’t behave like individual atoms. Researchers like to think of superfluid helium as a mixture of two fluids, one normal and one superfluid, which allows it to behave the way it does. But if you stir the helium like coffee and the normal liquid will feel the friction in the motion, meaning the superfluid mixture will feel it too.
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