Saturday night Martin P. Haspang, Kåre H. Jensen and I played around with cornstarch and water. Mixed together this will create a non-newtonian fluid. This fluid appears almost solid when high stresses are applied such as a hit with a finger or spoon. With lower stresses the fluid will behave as a fluid. In this video my girlfriend demonstrating the features of the fluid:
In an article from 2004 such a fluid is put on a plate oscillating with a frequency above 60 Hz. In the article and the corresponding video the fluid expresses quite amazing qualities such repulsive holes and the growth of fingers on the surface.
F. Merkt, R.D. Deegan, D. Goldman, E. Rericha, & H.L. Swinney, “Persistent holes in a fluid”, Phys. Rev. Lett. 92 184501 (2004).
Original paper: hole_PRL.pdf (973 kB).
Original video: Fingers and Holes in a Shaken Cornstarch solution. [youtube.com]
Inspired by viral video video we wanted to recreate a the dancing viscous fingers using some older speakers and a tone generator. Unfortunately I forgot to bring my DSLR camera for the video shoot so we were limited to 30 seconds in low quality. After playing around with two speakers (and ultimately destroy them) we finally saw the dancing fingers on the third and final speaker.
The critical feature was the frequency and the amplitude of the speaker since a good amount of energy is induced to the fluid. When increasing the frequency on this speakers the amplitude dropped and needed to be amplified. In the original article a phase diagram with acceleration and frequency is provided for those who would like to recreate the experiment themselves.