Wednesday, November 22, 2006

oobleck and glurch

I came across this completely (well, to me anyway) fascinating clip on YouTube today: inauspicious beginnings with some bloke stirring a petri dish of cornstarch with a pencil, but it gets seriously weird towards the end. The crazy phenomenon in the last phase of the experiment is called the "Lovecraftian tentacle effect", apparently, a perfectly apt description (assuming you've read some Lovecraft).

It's all to do with non-Newtonian fluids, which display counter-intuitive effects like getting thicker when you stir them (and then thinner again when you stop). The cornstarch one (try mixing a load of cornflour with some water) is used in school science lessons to illustrate non-standard liquid behaviour. It's colloquially called oobleck, apparently, and is often used for teaching purposes in conjunction with another non-standard liquid called glurch. Great names! A note of caution though: section II of the article perpetuates the myth about glass windows thickening at the bottom over time because of the glass flowing like a (highly viscous) liquid. This is generally accepted not to be true - if you want an interesting example of a true super-viscous liquid try this.

If you make custard with cornflour, you can walk on it, as this clip proves. Just don't stop or you'll sink.


Anonymous said...

Spooky. I was reading about Oobleck etc. just the other day on the DansData Blog. Fascinating stuff.

electrichalibut said...

Well, not that spooky, as I had a snoop round there earlier after following the link from your blog, and that put me in mind of the custard thing. So who is this Dan person?

Anonymous said...

He is Australian, which probably makes him the Auld Enemy for the duration of The Hashes.

His blog is great fun and his reviews website is choc-full with fascinating and interesting technobabble. And cats.