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The Secret of Cornstarch Physics
sciencehabit writes "Filling a small swimming pool with cornstarch and water has long been a physicist's party trick. Step onto it slowly and you'll sink, but run across quickly and the oozy mixture will support your weight — almost as though it has turned from liquid to solid. Several reasons have been offered for the phenomenon, but now researchers believe they have the real answer. The key to figuring things out: plunging a 370-gram aluminum rod from a slingshot at around 1 meter per second into a cornstarch suspension." One meter per second doesn't seem very fast for anything launched by a slingshot, but any speed is good as long as it advances important knowledge like this.
Penn Jillette once almost drowned a midget while wrestling nude in a swimming pool filled with cornstarch. Oh and non-newtonien liquid bla, bla, etc.
"Have you ever thought about just turning off the TV, sitting down with your kids, and hitting them?"
Has anyone made the Sugru clone by mixing silicone I caulk and cornstarch (I think ratios are flexible, up to 1:3 with reasonable cure times)?
As I understand it, the cornstarch absorbs the water and accelerates the silicone cure time, enabling a cure phase where it is hand-moldable like Sugru?
I have a box of corn starch and two tubes of silicone waiting at home for me to try this. There's an instructable for this that focuses on a different project but a lot of the project is spent on making this hand-moldable silicone.
I use Harvey plumber's epoxy (moldable, like clay, but gets rock hard) all the time and I've always wanted a hand-moldable product that would have the finished consistency of silicone. Silicone itself is too goopy and cures poorly if very thick.
Sugru solves this, but its expensive. There are other two-part silicones that can be bought, but they are expensive, too, and this method seems pretty simple and inexpensive (I think I bought two full-size tubes of GE brand Silicone I and a box of cornstarch for about $6, certainly less than $10 total).
I really wonder about that slingshot... why not just drop the bar from 5cm above? 1m/s is the speed it reaches when dropped from that height.
(actually, I think the journalists fucked up the numbers again)
In Rod We Trust.
(or, more appropriate to the topic : In, Rod We Thrust).
This or it's a non-newtonian server and I clicked so fast I couldn't enter.
I thought this was well understood and have explained it to my nieces/nephews and many others.
Corn starch as packaged for sale consists of VERY small grains (see http://ars.els-cdn.com/content/image/1-s2.0-S0144861705005059-gr3.jpg). When mixed with water in appropriate proportions, they exhibit the same behavior as sand at the beach's edge where it will apear to dry when stepped on and when the pressure is removed will return to being very wet.
This has to do with dense packing behavior: When undisturbed, the particles naturally form a relatively dense packing due to it's low energy configuration. watter fills the space beween the particles. By disturbing the dense packing by applying an external force, the space beween particles increases alowing for more water to be stored in the inter-particle space. The natural dense packing will occur once the disruptive forces have disipated, so to remain in the more 'solid' state, the dense-packing arangement must constantly be disturbed.
If this research is aimed at the reason for the natural dense-packing in the first place, I thought that was also well understood. Am I missing something?
> "One meter per second doesn't seem very fast for anything launched by a slingshot, but any speed is good as long as it advances important knowledge like this."
This is how you chose to contribute to the submission? Really?
Traditional Story
In the Old Testament, Moses told the Israelites not to leaven their bread, and subsequently led them safely across the Red Sea. When the Egyptians pursued them, they drowned.
What Really Happened
Obviously, Moses had someone go around and collect all the baking powder (which these days is made from sodium bicarbonate, tartaric acid and cornstarch). Some kid started asking a bunch of questions that irritated Moses, such as, "Why is this night different from all other nights?" He explained that they were leaving Egypt. When the child asked, "Why are we eating unleavened bread?" Moses replied, "uh, because we're in a hurry, kid. Stop asking questions!" He then had the Israelites' baking powder dumped into the sea so his people could run across it. However, since it wasn't pure cornstarch, it was unstable and collapsed by the time the Egyptians tried to cross.
It all makes sense now. God I love mixing science and religion. It's a lot like mixing water and cornstarch. Anything holds up surprisingly well if you run through it fast enough.