September 27, 2004
The physics of goo
Back when he was writing the Principia Mathematica, Isaac Newton argued with his pal Chistiaan Hyugens about an interesting question: Would someone swim faster through water or through a thick, viscous goo? Newton bet you'd go slower; Hyugens argued the opposite. Newton decided to put both viewpoints in the Principia, since he couldn't resolve it. There seemed to be no way to test it: Who was going to go to the trouble of constructing a massive tank and filling it with goo?
A professor at the University of Minnesota, as it turns out. Edward Cussler took 300 kilograms of guar gum, a thickening agent found in salad dressing, and dumped it into a 25-meter swimming pool on campus. The result was a goo twice as thick as water. He then -- and I cannot imagine what these conversations would have been like -- convinced 16 volunteers to jump in a swim a few laps.
"The fluid," as Cussler told Nature.com, "looked like snot. I don't know how to describe it any more poetically."
The result? Turns out Hyugens was right: The swimmers didn't go any faster in water than in the goo. Cussler says that's because that while the goo generates more drag on your body, it also lets you generate more force with each push and kick. However, as you'd expect ...
... the most troublesome part of the experiment was getting permission to do it in the first place. Cussler and Gettelfinger had to obtain 22 separate kinds of approval, including persuading the local authorities that it was okay to put their syrup down the drain afterwards.
But it was worth the hassle, Cussler says, not least because his quest for an answer made him something of a celebrity on campus. "The whole university was arguing about it," he recalls. "It was absolutely hilarious."
(Thanks to Stephen for this one!)
Posted by Clive Thompson at September 27, 2004 02:15 AM
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I would expect that this "speed" gained by increased force is eventually decreased as the viscosity is increased. I don't fully understand the technical aspects of viscosity, but I can imagine a swimmer making very little progress in molasses or honey as their strength is used up in overcoming drag.
I give Cussler big points for finally laying *this* one to rest...and actually, it kind of sounds like fun swimming in goo.
He might have had an easier time doing the experiment had he known another scientific truth: it's easier to seek forgiveness than to get permission...
Heh. Yes, that one is definitely requiring replicatible results.
Alfred, yeah, I'd suspect the same thing -- wouldn't there be a point of diminishing returns on the viscosity/speed equation?
the physical facts of moving through a medium 1000 times as dense as air (water) is such that resistance is cubed at the surface and squared under the surface...if asked to double one's speed throught the water, resistance would be 2x2=4 under to surface, but 2x2x2=8 times the resistance at the surface...and all this is with water at a temp between 78 and 80 degrees F. In fact this temperature range if required for sanctioned competitions to ensure appropriate density as colder water becomes more dense and swimming is slower.
I can not imagine moving through a medium with much greater viscosity than water as we know it.
Okay, now you've made me never want to swim again my life. Not that that's a bad thing.
This is an example of the kind of experiment where the subjects know what's going on and this knowledge will effect their swimming behavior. Because of this confounding variable, I refuse to believe this has been settled.
