Motivated By Curiosity And A Desire For The Truth – Part Twenty Two
October 31, 2016
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We use the phrase like moving through treacle as a simile for doing something slowly and with difficulty. For the enquiring mind, the obvious question is – is it really slower than moving through any other form of liquid? It is a question that has occupied much greater minds than mine. In the 17th century Isaac Newton and Christiaan Huygens considered the question, with Newton arguing that an object’s speed would be affected by the viscosity of the fluid through which it was travelling. Huygens took the contrary view – that it would not make a jot of difference. Newton was sufficiently troubled by his colleague’s assertion that he included both theories in his Principia Mathematica. Not very helpful!
In 2004 Edward Cussler of the University of Minnesota published a paper in the ever popular American Institute of Chemical Engineers Journal in which he described the results of his researches, into whether humans swim more slowly in syrup than in water, ably assisted by a student competitive swimmer, Brian Gettelfinger. Their syrup of choice was guar gum or guaran, which comes from the guar bean, native to India. It is used commercially in the food industry primarily because it binds water and it only takes small amounts to thicken. Guar is often used in ice cream to improve texture and in gluten-free baking to replace some of the structure lost by removing the glutens.
When you consider it there are a host of problems to be overcome if you adopt the empirical approach to the problem. You need to find sympathetic owners of a swimming pool who will allow you to fill it with syrup, you need enough of the stuff to fill the pool and then you need to work out how to dispose of it after the experiment is over. Showing the tenacity of a determined scientist, Cussler secured the twenty two separate permissions he needed to conduct the experiment and managed to convince the local authority that it was perfectly safe to empty the syrup down the drains.
So the stage was set for the experiment. Two 25 metre swimming pools were used, one with ordinary water and the other mixed with more than 300 kilograms of guar syrup, producing a gloopy liquid twice the thickness of water. Sixteen volunteers, some competitive and others recreational swimmers, took part, deploying the same strokes in each of the pools. What the researchers found was that irrespective of the strokes used, the swimmers’ times differed by no more than 4%. What is more neither water nor syrup produced consistently faster times. So Huygens was right.
It seems that when you are in syrup you experience more friction from your movement – what is known as viscous drag – you generate more forwards force from each stroke. In other words, the two cancel each other out. For humans what determines the speed at which you swim at is not the liquid you are swimming in but the shape you adopt. Once the effects of thrust and friction have cancelled themselves out, the predominant force is form drag, the frontal area presented by the body. The perfect swimmer has powerful muscles but a narrow frontal profile.
However, below a certain threshold of speed and size, viscous drag becomes the dominant force and in those circumstances swimming through syrup would be more difficult than through water. Just ask some bacteria.
So now we know!