Is it a liquid? Can it be both? In this activity, you will make a substance that is similar to quicksand—but much more fun. Play around with it and find out how it acts differently from a normal liquid and a normal solid. Other, more familiar substances change states from solids to liquids to gases when we change the temperature, such as freezing water into ice or boiling it away into steam.
But this simple mixture shows how changes in pressure, instead of temperature, can change the properties of some materials. Background Applying pressure to the mixture increases its viscosity thickness.
A quick tap on the surface of Oobleck will make it feel hard, because it forces the cornstarch particles together. But dip your hand slowly into the mix, and see what happens—your fingers slide in as easily as through water. Moving slowly gives the cornstarch particles time to move out of the way. Oobleck and other pressure-dependent substances such as Silly Putty and quicksand are not liquids such as water or oil.
They are known as non-Newtonian fluids. This substance's funny name comes from a Dr. Seuss book called Bartholomew and the Oobleck. But such substances actually just need a bit of a kick to get flowing. You must provide enough force to overcome the internal friction that keeps them stationary, such as by giving them a squeeze, which lowers their viscosity. They can then be easily extruded from a tube, bottle, or packet.
When you mix cornstarch into water, the starchy grains become suspended in the liquid, creating a substance with weird non-Newtonian abilities. When you apply pressure to oobleck, it works the opposite of the previous examples: The liquid becomes more viscous, not less. At the places you apply force, the cornstarch particles get mashed together, trapping water molecules between them, and oobleck temporarily turns into a semi-solid material. This force can be anything, including the sound vibrations from music speakers or a rapidly shaking container, as in the video at the top of this post.
That particular experiment really highlights oobleck's strangeness. The vibrating dish creates bumpy Faraday waves in the liquid. A puff of air introduced into this system creates a hole in the oobleck that just hangs out, not disappearing like you would expect. Speed up the vibrations and the hole will turn into a writhing mass that slowly takes over the entire surface of the oobleck. I don't know about you, but I can't watch that video without some internal WTF alarms going off.
When you run your fingers slowly through cornstarch and water, it acts like a liquid , but apply rapid force, and it solidifies, bends and even tears. After seeing a scientific talk about oobleck's properties, Kamrin and his colleagues launched a "very healthy" internal debate over how cornstarch and water might differ from other wet, granular materials. The scientist and his team typically focus on the flow of sand, gravel and other industrial materials.
But cornstarch is different, he said, largely because the particles are so tiny. Cornstarch particles are a micron to 10 microns in size, smaller than the diameter of a human hair. At this size, particles are susceptible to the tiniest of thermal and electric forces, Kamrin said. As a result, cornstarch particles in water actually repel each other slightly, held apart by forces too weak to impact something as large as a grain of sand.
What advantages does this type of liquid have? Latex paint and ketchup are non-Newtonian fluids of the opposite variety to oobleck. Paint will flow off a brush onto a wall but won't easily drip or run. Ketchup won't pour out of containers unless smacked, squeezed or shaken.
Oobleck is a non-Newtonian fluids of the opposite variety ketchup, and in a bottle it should behave opposite to ketchup- it will flow out easily when inverted but won't flow when you smack, squeeze or shake it.
Give it a go! Try to paint with oobleck, it will be difficult to smear and will then run away. Related Resources States of Matter States of matter can be more than just your average solids, liquids and gases! When water turns into snow, is….
Goo Who knew that chemistry could be so wonderfully gooey?
0コメント