Science In The City SIC-Bullet Proof Goo
SIC-Bullet Proof Goo
Science In The City Bullet Proof Goo
DEAR SCIENCE WORLD,
At your science centre I saw a goopy liquid that turned solid on impact. Do you know what that was?
Unidentified Mystery Caller
Answering a phone call from a stranger at work is always an adventure. It could be an inventor of a machine that transports you to the fifth dimension, or a frustrated teacher trying to power a light bulb with potatoes. The other day my phone rang and the conversation began with a question: “I saw some weird liquid at TELUS World of Science that becomes hard when you hit it. What was that stuff?”
I knew right away he was referring to Oobleck. We create it by mixing cornstarch and water. The resulting substance is a peculiar fluid that flows with gentle manipulation but stiffens under stress. To demonstrate the wonders of Oobleck, I slowly sink a hand into the stuff and then strike the wet surface with a hammer. The starch molecules lock together upon impact and protect my fragile fingers under a cement-like surface. With a small pool of Oobleck, you can even try jumping on top of it! But be careful — once your feet sink in you won’t be able to jump out!
Oobleck may take its funny name from Dr. Seuss, but scientists describe it more seriously as a “non-Newtonian fluid with shear dependent viscosity.” Isaac Newton defined normal liquids as having consistent flow behaviour affected only by temperature or pressure; so fluids that change their resistance to flow (viscosity) under stress are not ‘normal’. Some of these fluids get runnier when stress is applied, like paint, toothpaste and slug mucus. Some get thicker, like quicksand and Oobleck.
After I provided the caller with our recipe and explanation, he pitched his idea to me: “I think I could make sports padding with this stuff. It would be flexible when running but would harden and disperse the blow of an impact.” I had to hand it to him; it was a use that never occurred to me. I cautioned that Oobleck is heavy and messy but wished him well in his inventive pursuits.
Curiosity sparked, I did some research and found liquid armour had already been dreamed up by Larry Niven in his 1968 novel Neutron Star, and the Army Research Laboratory and University of Delaware secured a patent for inventing the real thing in 2006. They created a unique fabric combining Kevlar® fibres and silica in polyethylene glycol gel. Just like Oobleck, it is pliable until an impact causes the silica bits to jam together dispersing the force to a larger surface area. In tests, the liquid armour successfully resisted puncture, which even bullet proof vests can’t do.
So thank you, Unidentified Mystery Caller, for inspiring me with your creative curiosity and keeping me on my toes with the latest innovations. At least it wasn’t another call from the English lady who wanted to send our bike-powered generators to UK prisons in order to offset her electricity bill (true story!).
Rhoda Klein, Science World