There are still other varieties, too, which have different patterns of changing viscosity. Also in the thixotropic category as well as in your kitchen: ketchup and honey.
Some of them get runnier when under stress, such as Space Pen ink and paints that adhere to a brush when at rest but glide on easily when the brush is applied to a surface.
Going with the Flowīut not all non-Newtonian fluids behave this way. Stir more slowly, and it flows more easily. Assuming the proportion of starch to water is right, the solution gets suddenly thick and firm when force is applied to it, as you may have noticed when trying to stir it when preparing a sauce. You’ve probably made a cornstarch-and-water mixture lots of times in your own kitchen, and if you made enough of it, you too could walk across its surface. Non-Newtonian fluids range from the exotic to the mundane. (See YouTube for a long list of videos featuring non-Newtonian fluid experiments.) And sure enough, the ink from my Space Pen is in the same category.
These are just a couple of the many wacky properties exhibited by non-Newtonian fluids-substances that change their viscosity in reaction to stress. ( Mythbusters also did a segment on this phenomenon.) Or some other guys taking a handful of the same liquid goop and slapping it into solid balls, which then turn back into liquid as soon as the agitation stops. Purple Ink on my blog.)īack in 2006, some very cool videos started making the rounds: people doing stunts with something called “ non-Newtonian fluids.” If you’re not an engineer, that may not sound very intriguing, until you look at guys running across the surface of a vat filled with a solution of cornstarch and water, but sinking into it when they stand still. (As spiffy as that is, some Space Pen ink turns out to have surprising problems, which you can read about in Space Pens vs. It’s liquid just long enough to flow onto the paper, and then it turns semisolid again. These pens, legendary for being able to write underwater, in zero gravity, in a vacuum, or in just about any other situation, use a special thixotropic ink, a substance that’s normally in a gel state but which turns into a liquid when it’s agitated-that is, when the ball rolls against it. Pascal, Meet FisherĪlthough that little snippet of knowledge has stayed with me all this time, that marked the extent of what I knew about fluid mechanics until I wrote an article here about Space Pens. The same effect has applications in everything from scuba diving to ventilation systems and dam construction. This is the principle that enables hydraulic presses to work-a small amount of force applied to a piston pushing down on fluid can exert much more force on a larger connected piston, making it sort of like a liquid lever.
Pascal’s Law describes the behavior of fluids in a closed system, and says, to oversimplify somewhat, that the pressure the fluids exert is always the same throughout the system. For reasons I no longer recall, the topic I chose was Pascal’s Law, and I must have prepared well for that 10-minute presentation, because I could probably stand up and give pretty much the same talk today, even though I never went on to study any more about it. One of those was a report I did for my ninth-grade science class. But a few pleasant moments do stand out in my memory. That was an unpleasant time in my life for all the usual reasons, and thankfully most of it is now a dim blur. Like many people, I’ve tried hard to forget my days in junior high school.
0 kommentar(er)
