Oobleck

March 6, 2007

What if I told you I could stop bullets—even the armor piercing kind—with a mixture of cornstarch and water? You’d probably call me a lunatic, but it’s true…sort of.

Oobleck, was discovered a long time ago, but I only heard about it yesterday on Digg. Some of you may have heard the word before if you ever read Dr. Seuss (see the Wikipedia entry). Oobleck is actually a very interesting exercise in physics: it is a non-Newtonian fluid. In other words, it doesn’t act like water (a Newtonian liquid) particularly with respect to pressure.

Let’s take a pool as an example. If you jump feet-first into a pool, you will penetrate the surface because the pressure you’re body exerts on the surface of the water causes it to part. Duh, right? Well, if you jump feet-first into a pool of Oobleck, you’ll just bounce. This has the amazing implication that you can actually run across a pool of Oobleck. Don’t believe me? Watch the video below, it’s really quite impressive.

So how does this stuff work? Basically, when you mix cornstarch and water in the appropriate quantities and at the appropriate temperature, it forms a fluid that reacts to pressure in a unique way. In the absence of pressure, it basically acts just like water. When you apply enough pressure to it, though, it solidifies temporarily. It has to do with the crystalline structure changing under the pressure.

Naturally this has tremendous implications for the military. They are already developing and testing something similar that uses more advanced materials (I imagine cornstrach wouldn’t last too long—or smell very good, for that matter—on a desert tour). According to the article:

The liquid [inside the vests], polyethylene glycol, is non-toxic, and can withstand a wide range of temperatures. Hard, nano-particles of silica are the other components of STF. This combination of flowable and hard components results in a material with unusual properties.

“During normal handling, the STF is very deformable and flows like a liquid. However, once a bullet or frag hits the vest, it transitions to a rigid material, which prevents the projectile from penetrating the Soldier’s body,” said Dr. Eric Wetzel, a mechanical engineer from the Weapons and Materials Research Directorate who heads the project team.

STF’s has a variety of other implications as well, within and without the military. Wetzel mentions using it in soldier’s fatigues (which really need to be flexible, but can’t currently be protected), in bomb blankets to cover suspicious packages or unexploded ordinance, liquid armor could even be applied to jump boots to stiffen during impact and support the ankles. This leads to the fact that STFs can also be used in extreme sports. Daring skiiers and snowboarders would benefit tremendously from flexible body armor.

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