Related watching: oobleck , TED Ed , the incredible physics of ants , and more about that sugar in your ketchup. This Webby award-winning video collection exists to help teachers, librarians, and families spark kid wonder and curiosity. TKSST features smarter, more meaningful content than what's usually served up by YouTube's algorithms, and amplifies the creators who make that content.
Curated, kid-friendly, independently-published. Support this mission by becoming a sustaining member today. Get smart curated videos delivered to your inbox. In fact, one example of a common shear-thickening substance can be found in the kitchen: cornstarch mixed with water that forms a paste.
The mixture is fairly easy to stir at a moderate speed,. But when the speed picks up, the viscosity of the mixture increases until it finally becomes so firm that the stirring spoon gets stuck. This starch-water mixture behaves similarly to quicksand. Under gentle force, the sand grains slide past one another because they are lubricated by water. Sudden pressure displaces the water from the gaps and forces the solid components together, dramatically increasing the resistance.
As with quicksand, starch molecules are separated by a layer of water. And when strong forces bring them into contact, the mixture coalesces. The food industry has found a different way to deal with the vexing quality of ketchup: The condiment is now available in flexible plastic bottles. Just a slight squeeze is enough to overcome the resistance of the sauce. This solution certainly simplifies handling—but the sport of getting the sauce out of a bottle, and its moment of triumph when done cleanly, is lost.
This article originally appeared in Spektrum der Wissenschaft and was reproduced with permission. He has been writing about everyday physical phenomena for Spektrum der Wissenschaft since Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Discover World-Changing Science. Turn the bottle upside down still with the lid on and thrust downward at high speeds, accelerating both the ketchup and the bottle.
Swiftly stopping the bottle should slump the sauce into the neck. A full bottle will have the weight of the sauce pushing down whenever the bottle is tilted, whereas a nearly empty bottle will need some help. Increase the angle until sauce begins to flow. If it does not flow once the bottle is almost upside down, there is not enough weight of sauce left to induce flow.
The trick is to get the sauce flowing, but not too fast. Start by pointing the open end of the bottle toward your food at an angle of around 45 degrees with one hand around the bottleneck, and the other delivering gentle but firm taps on the bottom of the bottle. Increase the force of the taps until you balance the force applied with the mechanical strength of the sauce in order to get it to flow.
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