More Solid When Disturbed
I learned something today about non-Newtonian liquids -- cornstarch and water!! Two different examples!!Walking on liquid!!
Speaker activated liquid!!
An interesting collection of these on YouTube!!
What's the principle behind this?
Comments
Listed in chronological order. Newest comments at the end.
Listed in chronological order. Newest comments at the end.
What's the principle behind this? It's MAGIC! 
Posted by Expat47 in Athens, Greece on 02/04 at 10:02 PM
This is one possible behavior that falls under the umbrella of "non-Newtonian fluids". Specifically, corn starch or sand (quicksand!) suspended in water is "shear thickening", which basically means that the harder and faster you push them, the thicker they seem.
Another common example is Silly Putty, which you can get in 50 pound quantities from Dow Corning. You may be familiar with the way that you can stretch it out slowly, but it "breaks" if you yank it. And, of course, there's the YouTube video showing what happens when you throw 50 pounds of it off of a parking deck.
As I understand it, all of these examples have some relatively coarse particulate material suspended (not dissolved!) in water. Essentially what's happening is that when you exert force on them hard and fast, the particles don't have enough room to get out of each other's way, and they temporarily form a rigid structure. The military is even investigating using this property in designing body armor that will be flexible under normal conditions, but which will momentarily "solidify" when struck by a bullet.
Another common example is Silly Putty, which you can get in 50 pound quantities from Dow Corning. You may be familiar with the way that you can stretch it out slowly, but it "breaks" if you yank it. And, of course, there's the YouTube video showing what happens when you throw 50 pounds of it off of a parking deck.
As I understand it, all of these examples have some relatively coarse particulate material suspended (not dissolved!) in water. Essentially what's happening is that when you exert force on them hard and fast, the particles don't have enough room to get out of each other's way, and they temporarily form a rigid structure. The military is even investigating using this property in designing body armor that will be flexible under normal conditions, but which will momentarily "solidify" when struck by a bullet.
Posted by John Armstrong in http://unapologetic.wordpress.com/ on 02/04 at 10:12 PM
be that as it may john, it still looks like magic!
Posted by patty on 02/05 at 05:25 AM
they were messing about with this in an episode of the big bang theory. very cool.
Posted by Nethie on 02/05 at 10:10 AM
The TV series [I]Numbers[/I] had this phenomenon as a tangent a couple of years ago.
Posted by Bill in Thun, Switzerland on 02/05 at 01:49 PM
Oobleck
Posted by Robb on 02/05 at 03:36 PM
great discovery channel show MB(urbanlegend testers) did an episode a while back! try a little pinch and clump it up with a few drops of water in your hand...have fun
Posted by him in US on 02/05 at 07:59 PM
MythBusters rocks!!
Posted by MohawkWarrior on 02/05 at 08:52 PM
I believe both the American show, Mythbusters, and its less serious British counter part Brianiac have both done very similar stuff with custard
Posted by Jake on 02/06 at 03:50 AM
custard? "today we have a delicious experiment..."
Posted by patty on 02/06 at 08:55 AM
Part of the reason for this behaviour is that water becomes less viscous under pressure, most liquids become more so. This means that when compressed the water is more quickly able to run away from the point of contact and can sometimes leave the solid particles with too little liquid suspension to flow easily. If you make a similar mix of cornstarch and cooking oil, you don't get this effect, just a sticky, but Newtonian, mess.
Posted by Dumbfounded on 02/08 at 07:53 AM
Thixotropy --
John Armstrong and Dumbfounded have the concept right.
http://www.questia.com/read/117012268?title=Colloid
http://en.wikipedia.org/wiki/Thixotropy
Regards,
Professor Music
John Armstrong and Dumbfounded have the concept right.
http://www.questia.com/read/117012268?title=Colloid
http://en.wikipedia.org/wiki/Thixotropy
Regards,
Professor Music
Posted by Professor Music on 02/08 at 10:28 PM
http://en.wikipedia.org/wiki/Oobleck
Posted by Robb on 02/08 at 11:07 PM
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Category: Science