Post by thread:[EE] physiscs experiment "the solid liquid"

On Sat, Jun 02, 2007 at 12:31:57PM -0700, Vasile Surducan wrote: > OT/POT/NOT category for the "upside down world" > > Show this to your childrens or friends: > > Mix 1 part water with 2 parts starch > > The mixture looks liquid but you can't immerse your finger inside. > Taking out the content with a spoon it's solid, droping down in the > bowl it's liquid. > The perfect experiment for physics class. Yep, that is a very interesting mixture! If anyone wants to do more research about it, this is often called "oblick"; though there are many similar spellings. Looking up "non-newtonian fluid" will result in further info. I've recently read that this kink of substance is being looked at to create bullet-proof vests that are light and flexable. Matthew -- "If you hate your parents, the man or the establishment, don't show them up by getting wasted and wrapping your car around a tree. If you really want to rebel against your parents: outearn them, outlive them, and know more than they do." -- Henry Rollins

> OT/POT/NOT category for the "upside down world" > > Show this to your childrens or friends: > > Mix 1 part water with 2 parts starch > > The mixture looks liquid but you can't immerse your finger inside. > Taking out the content with a spoon it's solid, droping down in the > bowl it's liquid. > The perfect experiment for physics class. It sounds like Vasile and I at least sometimes think alike :-) I discovered this some years ago while cooking :-). Here the material I'd recommend is what we call Cornflour. I was thinking just a few days ago, after having encountered an ad for the "Monsterpod" camera support, that a contained cornflour mix MAY make a suitable mouldable base for a camera support. Able to be shaped but rigid against the camera weight. Quite how one would manage this in detail is "yet to be determined" :-) Russell

> Yep, that is a very interesting mixture! If anyone wants to do more > research > about it, this is often called "oblick"; though there are many > similar > spellings. Looking up "non-newtonian fluid" will result in further > info. I've recently read that this kink of substance is being looked > at to > create bullet-proof vests that are light and flexable. http://en.wikipedia.org/wiki/Non-Newtonian_fluid I wondered at the time how cornflour would work in bullet proof vests :-) "Bullet proof" vests. http://en.wikipedia.org/wiki/Body_armor Then there's Glurch ... :-) Oobleck, Glurch, Slime, Silly putty. Enjoy http://www.squarewheels.com/content/gackstuff.html O & G http://www.extension.iastate.edu/e-set/science_is_here/glurch.html http://www.dctech.com/physics/features/0901.php __________________ >From 1st ref above: A non-Newtonian fluid is a fluid in which the viscosity changes with the applied strain rate. As a result, non-Newtonian fluids may not have a well-defined viscosity. Although the concept of viscosity is commonly used to characterize a material, it can be inadequate to describe the mechanical behavior of a substance, particularly non-Newtonian fluids. They are best studied through several other rheological properties which relate the relations between the stress and strain tensors under many different flow conditions, such as oscillatory shear, or extensional flow which are measured using different devices or rheometers. The rheological properties are better studied using tensor-valued constitutive equations, which are common in the field of continuum mechanics. And: An inexpensive, non-toxic sample of a non-Newtonian fluid sometimes known as oobleck can be made very easily by adding corn starch (cornflour) to a cup of water. Add the starch in small portions and stir it in slowly. When the suspension nears the critical concentration - becoming like single cream (light cream) in consistency - the so called "shear thickening" property of this non-Newtonian fluid becomes apparent. The application of force - for example by stabbing the surface with a finger, or rapidly inverting the container holding it - leads to the fluid behaving like a solid rather than a liquid. More gentle treatment, such as slowly inserting a spoon, will leave it in its liquid state. Trying to jerk the spoon back out again, however, will trigger the return of the temporary solid state. A person moving quickly and/or applying sufficient force with his feet can literally walk across such a liquid. Shear thickening fluids of this sort are being researched for bullet resistant body armor, useful for their ability to absorb the energy of a high velocity projectile impact but remain soft and flexible while worn. A familiar example of the opposite, a shear-thinning fluid, is paint: one wants the paint to flow readily off the brush when it is being applied to the surface being painted, but not to drip excessively.

> > The mixture looks liquid but you can't immerse your finger inside. > > Taking out the content with a spoon it's solid, droping down in the > > bowl it's liquid. > > The perfect experiment for physics class. > > It sounds like Vasile and I at least sometimes think alike :-) > > I discovered this some years ago while cooking :-). > Here the material I'd recommend is what we call Cornflour. > > I was thinking just a few days ago, after having encountered > an ad for the "Monsterpod" camera support, that a contained > cornflour mix MAY make a suitable mouldable base for a camera > support. Able to be shaped but rigid against the camera > weight. Quite how one would manage this in detail is "yet to > be determined" :-) Years ago (like 25) I saw a science programme about a liquid that would solidify when a current passed thru it. They thought it would make a neat brake (vehicle), but I think a clutch or safety cutout would have been a better use. As usual with these things, it has never been seen since. Tony

On 6/2/07, Peter P. <spam_OUTplpeter2006TakeThisOuTyahoo.com> wrote: > Vasile Surducan <piclist9 <at> gmail.com> writes: > > > > OT/POT/NOT category for the "upside down world" > > > > Show this to your childrens or friends: > > > > Mix 1 part water with 2 parts starch > > > > The mixture looks liquid but you can't immerse your finger inside. > > Taking out the content with a spoon it's solid, droping down in the > > bowl it's liquid. > > The perfect experiment for physics class. > > But only corn starch works exactly like that. Try this with a corn starch :) : http://www.youtube.com/watch?v=f2XQ97XHjVw&mode=related&search= How reacts: http://www.youtube.com/watch?v=f2XQ97XHjVw&mode=related&search= and how looks waves on a loudspeaker: http://www.youtube.com/watch?v=WTCkVh9CWT8&mode=related&search= There is any doctor here being able to explain in a short formula the phenomena ? thx, Vasile

For camera purposes, there are various kinds of bean bags that contain either balls or structured 'beans' which stick to each other when vacuum is applied. It is also possible to have a 'bean bag' made of clay or plasticine (or Blu-Tack which is my favorite temporary glue material - I always have some Blu-Tack somewhere during prototyping, I even 'qualified' it for microwave use (2.4GHz) and high voltage (50kV/10mm)). The only disadvantage is weight. For non-Newtonian liquids (using magnetic control), see this: http://www.youtube.com/watch?v=qX6clRC21vo&mode=related&search= I once wasted some time looking similar things up on the web, and there are several. There are some where the 'sculpture' is achieved by moving ceramic magnets under (or above) a tray with ferrofluid. For a quick shot (!) of proper corn starch solution, a Twix or Mars bar with the top chocolate layer peeled off with a kife will yield a few grams, ready to use. Peter P.

On Mon, 2007-06-04 at 00:07 +1000, Tony Smith wrote: > Years ago (like 25) I saw a science programme about a liquid that would > solidify when a current passed thru it. They thought it would make a neat > brake (vehicle), but I think a clutch or safety cutout would have been a > better use. > > As usual with these things, it has never been seen since. I don't know about materials that solidify when current passes through them, but I do know of materials that change density in the presence of a magnetic field. Such a material is used in the suspension of the Corvette to allow tuning of the suspension with the flick of a switch. TTYL

"Tony Smith" writes: > Years ago (like 25) I saw a science programme about a liquid that would > solidify when a current passed thru it. They thought it would make a neat > brake (vehicle), but I think a clutch or safety cutout would have been a > better use. These are called "electrorealogical fluids." CNN used to have a program on the weekends called "Science and Technology Week" and one week they did a segment on these fluids. An electric field makes the molecules chain together which is what causes the solidification effect. They mentioned clutches and breaks, both. The catch is that it takes a rather high voltage to make a sufficient field for the corn starch solution to harden up. The report said that ER fluids had been known about since the 30's or 40's but nobody had done much with them. Martin McCormick WB5AGZ Stillwater, OK Systems Engineer OSU Information Technology Department Network Operations Group