A couple of years ago, a college roommate of mine brought home a pail of this stuff called Guck. He explained that it was a non-Newtonian fluid that was being sold as a kids toy. If you touch the stuff softly or move your hand through it slowly, it has a consistency slightly thicker than water. Moving quickly, slapping it or punching in turns it instantly to a solid. As soon as the force is no longer being applied, it turns back to liquid. I think I understand how this works, but what makes this non-Newtonian? What the heck is a Newtonian fluid?
-LabRat
ps. I’ve heard that this stuff can be made at home with a little kitchen chemistry. Bonus points to anyone who know how to do it.
And “non-Newtonian” is, as you’ve probably come to suspect, nothing more than marketing hype. There are such things as non-Newtonian fluids, such as neutronium (a relativistic fluid) and superfluid liquid helium (a quantum fluid), but I guarantee that you won’t mix up a batch of either of those in your kitchen.
Oh, and as an aside, I believe that the generic term for the stuff you describe is “ooblek”.
Naw, toothpaste is just a plain, ordinary liquid with a high (but constant) viscosity. The stuff mentioned in the OP changes viscosity with force. You can mix up some cornstarch and water (anyone remember the proportions?) and play around with some; it’s fun stuff.
Chronos, I’m pretty sure non-Newtonian has nothing to do with Newtonian physics per se but with Newtonian viscosity. Any fluid with a non-constant viscosity is “non-Newtonian.”
I suppose that, technically, neutronium might be non-Newtonian as well, but as we’ve never had a chance to play with a sample, I’d be hard pressed to judge either way
Hmm, apologies, I hadn’t read that web site as of when I’d posted my response. Ironically, if a Newtonian fluid is defined as having a constant viscosity, then the two examples I mentioned are Newtonian, having a constant viscosity of exactly zero. Rest assured, though, that ooblek and toothpaste both follow the laws of Newtonian physics nicely.
One of the classes of fluids described gave a bizarre name for fluids dependent on their history. They’re often termed memory fluids. They have interesting properties as they remember their previous behavior. I saw a film where they had this memory fluid in a beaker. They started pouring the stuff out of the beaker, like halfway down the outside, and then set the beaker back upright. The fluid poured back into the beaker. Cool!
A common non-Newtonian fluid mentioned is Jelly. Or Jell-o. Another one is tar. Tar is hard to the touch, seems like a solid. But if you set an object on a barrel of tar (open top) and leave it for a while, then come back later, you will find the tar has crept out of the way and the object has started to sink into the tar. http://www.madsci.org/posts/archives/mar97/856396884.Ph.r.html
Lots of answers already here but Lazarus hit the nail on the head with the non-Newtonian viscosity as the critical feature. Irishman is not entirely correct – memory fluids are generally non-Newtonian, but his examples aren’t all memory fluids. Tar is just a very viscous fluid. Jelly and jello are close calls, IMO. They’re not really liquids to begin with, but gels. They don’t really liquefy when stirred – they just break into smaller chunks. Admittedly some of the gel liquefies, but jell-o, at least, doesn’t re-set. It stays in chunks. So it’s more of a phase change than a characteristic of the liquid phase.
In my experience the most common non-Newtonian fluid is ketchup. Did you ever shake a ketchup bottle? poke a knife in it? hit the 57? These are all attempts to modify the ketchup’s “memory” so it will flow freely again.
Another is sour cream. Try spooning sour cream out of the container without stirring it, then repeat the experiment after stirring it vigorously. In the first case it is pretty solid, in the second it is pretty soft. Give it time to set and it gets firm again.
Finally a lot of latex paint, particularly house paint, is non-Newtonian. The label usually says “thixotropic” which is a particular kind of non-Newtonism. It’s thick until stirred but it thins nicely when shaken or stirred so it can be mixed and applied. But the “thickness” returns when it’s applied so that it covers well and doesn’t run or drip.
