Swimmers Don't Slow Down In Substance Twice As Thick As Water - How can this be true?

[astro]

Why is this the case? I find it difficult to believe you can swim as quickly though slime as through water. This defies (my) common sense expectation that the increased body drag of swimming through a thickened water based slime would offset whatever uncrease in pulling power the slime afforded your hands.

Swimmers Don’t Slow Down In Substance Twice As Thick As Water

University of Minnesota professor Ed Cussler has long wanted to know whether swimming in a substance thicker than water would slow someone down or allow them to swim faster.

With that in mind, Cussler coaxed 19 people, including some members of the university’s varsity swim team, to swim in water mixed with guar – a food thickener.

Logic suggests that a thicker substance would hinder swimming. Yet, as he watched the swimmers Monday, Cussler said, “It’s not clear to me that you’d go slower.”

The chemical engineering professor reasoned that the increased drag from the body might be countered, or even surpassed, by the hands’ ability to push harder against the increased resistance. With the university’s permission, the group mixed the guar – used to thicken ice cream, shampoo and other products – in a large garbage can and dumped it into a pool in Cooke Hall.

Cussler said the result was a dirty-looking liquid that was twice a thick as water. Each swimmer swam through 25 yards of the guar-thickened water, then took a break and swam the same distance in another pool – all while being timed.

After almost five hours of testing, preliminary results suggested that there was no difference between swimming speeds in the slime and in clear water.

[Padeye]

*Originally posted by astro *
Why is this the case? I find it difficult to believe you can swim as quickly though slime as through water. This defies (my) common sense expectation that the increased body drag of swimming through a thickened water based slime would offset whatever uncrease in pulling power the slime afforded your hands.

You seem to have answered your own question. If the increase in drag offsets the increase in thrust then the net gain is zero. That may or may not hold true for extremely viscous liquids. They’re swimming in slightly thickened water, not molasses.

[RickJay]

This does not strike me as being a terribly scientific experiment anyway. It may be that the speed isn’t much different in this particular case, but all we really know is that the swimmers didn’t seem to have different times between these two substances. IT’s not even clear to me how thick the substance was; the guy says “twice as thick” but did he measure it? What does he mean? We don’t know much else or what the function is for swimming speed as a function of viscosity, density, or anything else.

[Chronos]

This does not strike me as being a terribly scientific experiment anyway.

Well, we’re only seeing the pop-press version of it. Does anybody know a journal citation for it? I imagine that where the pop version says “twice as thick as water”, the peer-reviewed paper lists a viscosity in some standard units. And even without knowing exactly what the viscosity is, we do know that the speed is the same, since the swimmers cover the same distance in the same amount of time. My only quibble would be that the swimmers should be divided into two groups, one swimming the slime first and the other swimming the water first, so as to offset any effect of tiredness (and the experiment may even have done this, despite it not being mentioned in the pop article).

[MaryEFoo]

The thickening should increase the spread-finger effect, right?

Ie, if you pull your hand through the water with the fingers tight together like a spoon, it gives x amount of push, but you will find that by opening the fingers just a little, you have a broader paddle and get x+ amount of push. A swimmer might find that in thicker fluid, the fingers can be opened a little more for x++ push.