Oobleck

I thought I would join the YouTube bandwagon for this post. I used "science" as a search term and came up with one pretty cool example. (I do hope it's real, I found some fake science experiments in my search. The best by far is the Look Around You series.)

Here's a second video with a much bigger vat of cornstarch.

I looked around for some cornstarch articles on Google Scholar and PubMed but most of them had to do with eating cornstarch instead of walking on it.

Oobleck behaves as a non-newtonian fluid. Newtonian fluids react in a fixed proportion to pressure. If you push twice as hard, there's twice as much resistance. So when you try to step on water you push right through, there is nothing special about the molecules near your foot.

Non-newtonian fluids can have non-proportional reactions due to their sensitivity to gradients in flow speeds.

Oobleck gets incredibly viscous over small areas when strong pressure is applied. Oobleck molecules do care about their neighbors, a lot. If your foot is creating a change in the flow gradient, pushing one area of the liquid around a lot faster than the neighbors are being pushed, they stiffen up and push back. The reaction of the liquid isn't proportional to the pressure applied, it's complicated by the locals.

Okay, that hurt my brain so I'm not even going to attempt to explain what's happening in the video up top.

More fun with cornstarch (or sand or sugar). Sorry about the noise.

Now, let's combine crazy liquids with art (video). These artist/scientists used magnetic liquid in their sculpture. The magnetic fields are controlled by a computer that detects sound in the room. As a result, you get crazy movement when there's lots of noise. One of the artists, Sachiko Kodama, has a new solo project using magnetic liquids.

Magnetic liquids can be used in inkjet printers so that text or patterns can be read by machines.

Dampening is more common use for these liquids. Magnetic liquids can be manipulated by applying magnetic fields. When the field is off, the substance behaves as a liquid. With the application of the field the substance becomes thicker and resists motion. Some car shocks use this property to adjust stiffness depending on road conditions.