Well, you certainly know when it isn’t there … think walking on ice, or your car hydro-planing through puddles of water on the road as examples here.
So what happens when there really is zero friction. Impossible you say? Not with super fluids. In fact, that’s one of the reasons they are so investigated.
Take liquid helium for example (at extremely low temperatures of course). If you take it to within a degree or so of absolute zero on the Kelvin scale, it’s pretty darn hard to even keep it in a container. It either leaks out microscopic cracks, or because of surface tension properties it still possesses at those low temperatures, it physically climbs out the vertical sides of the container. Really!
On top of that, with zero friction – liquid helium won’t even spin when the container it’s in spins … no kidding.
Take a look at a couple videos that show some of these effects … the first is a fun one with a BBC TV star as narrator. Toward the end of the video (at about the 3 min mark), watch how the liquid helium leaks out of its container as if it had a really big crack in it. As can be seen by their surprise, that isn’t expected at all.
Not quite as exciting but still quite relevant is
Here, Daniel Kleppner of the MIT Physics Department (via Nova) does a pretty good job of describing how super fluid acts like interconnected wave packets – in a way that is quite understandable.
And then this article at Scientific American does a Great job of describing how a super fluid (Helium in this case) can actually climb the walls of its container. Amazing stuff …
Finally, take a look at what popsi.com provided for how super fluids act in a vacuum … tiny whirlpools that help keep single droplets of a super fluid stable, even when we think they probably shouldn’t.
Simply fascinating science and well worth a couple minutes to review.