The Cornflour Experiment
After seeing this done on many YouTube videos I just had to have a go myself, also as a synthesizer enthusiast I was also curious to try different wave shapes and combinations of waves to see if I could get anything different to happen.
Non-Newtonian Fluids - The root of this phenomena is that when you mix cornflour and water it becomes a non-newtonian fluid - a fluid whose viscosity is rate dependent. It's often termed silly putty since it appears to break the laws of physics and exhibits some rather strange properties.
Vibrated shear thickening fluids / Persistent holes in a fluid - Investigation including video footage on YouTube by Merkt/Deegan/Goldman/Rericha/Swinney of the University of Texas - Click here for full PDF
Waves - these are the mechanism through which sound, light, and pressure travel. Waves are everywhere when you look for them.
One example of waves interacting that I spotted is in water when the surface of the sea is disturbed by speed boats and water skiers going one-way around one of my local beaches. The boats come in from the right (looking out) and perform a nice curve around the bay then leave again on the left side. The bow waves from the boats spread out as normal causing waves on the beach etc, but also I noticed they meet in the middle of the semi-circular arc traveled by the boat, in this middle area the waves multiply and cancel out creating flat areas and large standing waves. This is due to constructive and deconstructive interference between the waves, when the peeks are together they multiply, when they are at opposite polarity the cancel out. These are Faraday waves.
My experiments, equipment and ingredients:
Cornflour and water mixture - No precise amounts, just mixed together in a bowl until it thickened enough to show the non-newtonian properties. It's weird stuff, once thickened it's strength is related to how much pressure you put upon it - under no pressure it behaves much the same as single cream; you can swill it around and pour it, but under stress it becomes hard like it has set; it fractures when scraped looking like a blomonge briefly before becoming liquid again.
Jamo 110w speaker - Standard home speaker with a fairly good bass response (which I did not mind getting dirty). Be warned; the effects are related to the amount of volume or SPLs that you apply - I got away without the neighbors complaining but I was creating vibrations at a volume comparable to making holes in a concrete wall with an electric drill. I've left the sound on the video so you get a rough idea. It maybe that you can use lower volumes with a more efficient setup but I was relying on intense vibrations between the baking tray and speaker casing which was intensely loud when you are sat next to it, in fact I doubt it was a coincidence that I had a chronic headache for about 24 hours after!
Tone generator - any will do including software tone generators and instruments that use the analogue style of synthesis where you can isolate a single oscillator. I used my Akai S01's preset sine wave detuned by -49 steps so the B under middle C would be exactly 120Hz. I tried using pulse/saw/tri waves which seamed to give a very similar response to sine waves, also I tried white and pink noise which did nothing. I also tried combinations of waves such as octaves and harmonics which upset the Faraday waves and caused them to be less stable.
Drinking straw - or similar, this is just so you can blow holes in the mixture and watch what happens.
Baking tray - Just an old round baking tray, I don't think the shape makes any difference though the Fourman page talks about the resonant frequency of his tray. I also tried using cling film layed over the speaker cone itself but, though this did work, it made more of a mess than anything.
My Results and Conclusions
I haven't done enough testing to be able to draw any reliable scientific conclusions yet really but these are the areas I was interested in:
Saw/Triangle/Square Waves - I tried several different wave shapes which seamed to give similar but more erratic results.
White/Pink noise - I noticed white and pink noise were available in a software tone generator which I'd used to confirm my frequencies. They both appeared to do nothing at all using the same setup and same volumes which make the sine waves come to life. I guess this is to be expected since there are no standing waves created, and no phase relationship.
Octaves and harmonies - I was hoping to get some new results using combinations of sine waves; which look great on the oscilloscope but have only negative effects on the experiment destabalizing the waves. It was these tests with multiple notes held down that helped make a mess in the studio, I'll be wiping little white dots off the walls for months!
Further Information and Resources:
- Michael Fourman - Cornflour Fingers - http://homepages.inf.ed.ac.uk/mfourman/fun/index.html
- The University of Texas investigates - http://chaos.ph.utexas.edu/research/vibrated_cornstarch.htm
- Frequencies for equal-tempered scale (musical notes) - www.phy.mtu.edu/~suits/notefreqs.html
- Spooky Cornstarch (and many other cool science tricks) - www.tesladownunder.com/interesting_stuff.htm