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The Viscosity of Water January 15, 2009

Posted by Chris Sullivan in Miscellany.
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I’ve been reading a little book about the Gulf Stream called The Gulf Stream by Stan Ulanski. Right now I’m up to page 64, and it mentioned that the viscosity of water at 4oF is twice that of the viscosity at 95F. It mentions this fact in relation to floating plankton, which not only must be buoyant, but must resist sinking by creating drag in the water. Plankton do this with “elaborate projections or feather like appendages (that) radiate outward from the body like the spokes on a wheel, effectively increasing the organism’s surface area”. He goes on to note that there are more of these decorations on warm water plankton than those which occupy colder waters, because the colder water with its greater viscosity increases the effectiveness of these appendages.

A table of water viscosities at various temperatures I found with google shows him to be right, and I’ve personally dived water from about 37F up to about 86F, which is a similar range of viscosities. The viscosity of water will have some impact on how quickly some things, including divers, will sink. Schlumberger published an educational experiment to measure the time to sink of a marble in shampoo at various temperatures. The differences were dramatic, although they did not mention the relative viscosities of the shampoo at these temperatures.

I also wonder what affect viscosity has on the speed of swimming, or even the speed of a diver propulsion vehicle. It might be hard to determine by experiment as other factors might get in the way like the apparel the diver wears in different temperatures or his swimming energy when cold or hot. Viscosity will have a greater effect on small things like plankton than large ones like divers, but I can’t help but wonder how changes in viscosity due to temperature affect diving.

My diving wishlist this year includes some surveyor’s tape for underwater measurements. Time permitting, I’m going to do some mapping in the already well mapped diving area in Big Bay Point and might do some timed swims at different temperatures. I’m going to wait until it gets a little warmer though. Today it’s about -30C (-22F) outside.

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