If you replace the water in a swimming pool with syrup and convince some of your colleagues to swim in it, will they swim slower or faster?
A swimmer and an engineer filled a swimming pool with syrup and timed several professional and recreational swimmers doing laps. Using rigorous scientific methods, they found that humans do not swim slower in syrup than in water. Lu and Tirth discuss this counterintuitive finding on S01E04 of the Recreational Science podcast (timecode 11:33):
Lu: The title of the study I’m presenting today is, “Will humans swim faster or slower in syrup?” This was published in 2004 in the journal Fluid Mechanics and Transport Phenomena, which is a very, very good journal.
Tirth: Long name.
Lu: And I think the title of the article speaks for itself. But what’s interesting is this article has a forward written by the editors of the journal: “the scientific and engineering principles that underlie chemical engineering can also be used to understand a wide variety of other phenomena including in areas not thought of as being central to our profession. As such, applications might be of interest to our readers, we will consider brief submissions for publication in this category as R&D notes. These submissions will undergo review and novelty will be an important factor in reaching an editorial decision. The first such article, ‘Will humans swim faster or slower in syrup?’ by Brian Gettlefinger and associate editor Ed Cusler, appears in this issue.”
Tirth: Yo, this is the perfect recreational science journal, man. They’re literally saying submit all your craziest stuff to us.
Lu: Yes. As long as one of the authors is the associate editor.
Tirth: Yes, exactly.
Lu: So will humans swim faster or slower in syrup? Do you have a guess?
Tirth: Yes, I do. Slower.
Lu: Oh, interesting. Well, I think you’ll be moderately surprised.
Tirth: Okay.
Lu: Here are the methods: they used guar gum to thicken swimming pool water. Guar is a type of bean, so this is a sugar extract from the bean. They chose guar gum because it’s food grade and it’s also hypoallergenic. It’s commonly used as a thickener in food. They also thought about using Xantham gum, but they couldn’t find any. They also considered using corn syrup, but they thought it might cause a strain on the city’s sewer system.
Tirth: They are very considerate.
Lu: They poured 310 kg of guar into a garbage can. The dimensions of the garbage can are 0.15 m3. And they stirred the mixture with a 1 kilowatt motor while pumping in pool water at a rate of 0.01 m3 per second until they filled up the garbage can. And then they poured this mixture into a swimming pool, the dimensions of which is 650 m3.
Tirth: I don’t understand any of these numbers.
Lu: They then stirred the mixture inside the pool for 36 hours with three submersible pumps each moving at a speed of at least 0.05 m3 per second. So the resulting solution they generated had a viscosity of 1.92 plus or minus 0.05 * 10-3 Pascal seconds. So the viscosity is about twice that of water, swimming pool water. And then they asked 10 competitive swimmers and six recreational swimmers to swim 25 yards in water, 50 yards in guar solution and then 25 yards again in water. So after all of this work, what did they find? Your guess is slower in guar.
Tirth: Slower, that’s right.
Lu: They actually found that there’s no difference in swimming speed.
Tirth: Wait, for the professionals and the recreationals?
Lu: For all 16 swimmers, there was no difference between regular water and guar gum.
Tirth: Wow. That’s crazy.
Lu: So their conclusion is that because human flow or human swimming is more turbulent and less laminar flow, that the viscosity of the swimming pool doesn’t really affect them that much.
Tirth: Uh-huh. Because it’s so inefficient to begin with.
Lu: Like, for instance, microorganisms swim in a more laminar way, and so they’re directly affected by the viscosity of the water, by the drag. But human are splashing around with arms and legs, right?
Tirth: Mhm. Yeah.
Lu: So you can more or less swim in like a ball pit.
Tirth: Yeah. That’s true.
Lu: So maybe viscosity doesn’t matter as much.
Tirth: As much.
Lu: In this case. But it still probably matters a little, right?
Tirth: Yeah, yeah.
Lu: Which brings me to my first criticism, which is guar, the solution they used is actually quite thin. So it’s only two times the viscosity of water, which is still not that viscous or thick. And they only had 16 swimmers. So this is probably an experiment that’s underpowered to detect a small difference in swimming speed. Underpowered meaning their sample size is too small to detect a small difference.
Tirth: Yes.
Lu: If they filled up the swimming pool with oatmeal, they’d probably find a difference.
Tirth: Yeah. Or crude oil.
Lu: Or crude oil. One good thing I liked about the paper is that their reporting of the methods is very rigorously. Very detailed. If you were to reproduce this study, you would have no problem reproducing exactly what they did.
Tirth: Yes. Right.
Lu: So in my opinion, great science.
Tirth: Yes, agreed.
Article citation
Gettelfinger & Cussler, 2004. Will humans swim faster or slower in syrup? AlChE Journal. https://aiche.onlinelibrary.wiley.com/doi/10.1002/aic.10389
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