Category Archives: Physics

Richard Feynman at the Thinking Machines Corporation

The Long Now Foundation re-published an essay Daniel Hillis wrote for Physics Today: Richard Feynman and the Connection Machine.

And speaking of Feynman: One of my favourite quotes about teaching can be found in the foreword to his Lectures on Physics:

“The power of instruction is seldom of much efficacy except in those happy dispositions where it is almost superfluous.” Edward Gibbon.

Non-Newtonian fluids, again.

Ask MetaFilter: Liquid Bounce.

“At the University of Texas, researchers have produced some amazing videos and photos of liquid bouncing on liquid. This was one of nature.com’s Images of the Year for 2007 (picture number 6, in the upper-right corner). The project report, along with pictures and videos, is found on their bouncing jet page, and it’s quite extraordinary both for the counter-intuitive nature of the phenomenon and the extremely low-tech production methods. You can even do it at home with little more than a lazy Susan and some silicone oil.”

Includes a link to vibrated shear thickening fluids.

(Previously: February 17, 2008, April 22, 2007.)

Non-Newtonian Fluids

Non-Newtonian fluids are fluids whose visosity changes according to the force which is applied to them. Stick your finger in slowly, and it behaves like a liquid, but bang it with a fist, and it behaves like it’s solid. Like in this film: Non-Newtonian fluid (Youtube link).

Or, more spectacularly, you can even walk on the liquid, like in this movie: Walking on a cornstarch-water-mixture (noisy Youtube link, in Spanish).

Of course, the best-known non-Newtonian fluid is Silly Putty, at least to Americans. By the way, I’ve never seen it for sale in Germany, but John VanDyk was kind enough to send me some years ago. Hi, John!

Non-Newtonian fluids have some interesting properties (the following are all Youtube links, except where noted):

Kaye Effect: Pour a thin stream of shampoo into a container, and a stream of shampoo might jump back up. This effect became famous when it was explained by a group of Dutch scientists last year, who produced a stunning video of the Kaye effect. See also Leaping Shampoo and the Stable Kaye Effect (PDF).

Fano Flow: the fluid can be syphoned tubeless – it seems to move upwards unsupported.

Weissenberg Effect: The fluid climbs up a rotating rod. You know this one from beating egg-whites with an electric mixer.

Barus Effect (aka Merrington Effect, Die Swell, and Extrudate Swell): After passing a small orifice the diameter of the liquid stream increases.

Liquid Rope Coil Effect: When the poured liquid reaches the surface, it seems to coil like a rope. You can demonstrate this one fairly easily with honey.

For the record

Für die Schüler, die mich beim Thema Radioaktivität im Physikunterricht immer fragen: “Bauen wir auch eine Atombombe?”, sei hier §328 des Strafgesetzbuches zitiert:

“§328 Unerlaubter Umgang mit radioaktiven Stoffen und anderen gefährlichen Stoffen und Gütern
(1) Mit Freiheitsstrafe bis zu fünf Jahren oder mit Geldstrafe wird bestraft,
1. wer ohne die erforderliche Genehmigung oder entgegen einer vollziehbaren Untersagung Kernbrennstoffe […] aufbewahrt, befördert, bearbeitet, verarbeitet oder sonst verwendet, einführt oder ausführt.
(2) Ebenso wird bestraft, wer […]
3. eine nukleare Explosion verursacht”.

Antwort auf die Schülerfrage: Nein.

Physics is fun!

I’m incredibly busy and buried in work right now, but what physics teacher could pass up such a wonderful link? Crayon Physics Kloonigames (“Monthly Experimental Games”). There is a ball and a star, and the goal is to get the ball to the star – by drawing physical objects that fall down, rotate or do other things. I watched the videoclip, and I really have to try it out once I’ve got time.

Link via Lehrerzimmer. Danke, Herr Rau!