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Comparing Sperm Whales To Sperm: A Swimming Contest

Friday, October 04, 2013 - 12:56 PM

Sperm whale and sperm Brad Pumell/YouTube

If you're a big, big whale with a gigantic tail swimming through water, nothing gets in your way, not the water, not the other fish, not nothin'. You are so much bigger than the water molecules around you, you move through the sea the way humans move through the air on a calm day — you just go. Whales, I imagine, don't think much about water.

Contemplating sperm

Brad Purnell/YouTube

But now, imagine yourself smaller. Much, much, much smaller. Instead of a sperm whale, let's make you, say — a human sperm, a teeny little critter with hardly any mass, and a very skinny, beating tail. All of a sudden you are much closer to the size of the water molecules around you.

Now that you're little, getting through water is a huge headache. You are wedged in among equal sized H2O thingies that slow you way, way down. A human sperm in water is like a car in an enormous traffic jam — barely able to move.

So how do the littlest things in life — sperm, bacteria, pond scum — get where they need to go? How to they find food? Cows don't sit in meadows waiting for grass to grow next to their mouths ...

Brad Purnell

No, little things are cleverer than that. Much, much cleverer, as you will see in this video, elegantly illustrated by Brad Purnell, narrated by Addison Anderson and thought up by Aatish Bhatia, here's how they do it.

I guess of all the moving strategies I've ever encountered, this one — used by a little Broadway billboard-ish critter that dazzles trills of rainbow colored light in the shallow ocean — is the craziest. It uses the same strategies Brad and Aatish describe ... but it seems to think it's a Rockette at Radio City Music Hall.

Comb jelly from Gulf of Mexico, at Texas State Aquarium.

Gregory G. Dimijan/Science Source

And I wrote about it here.


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Comments [4]


For those interested in digging into this issue a little more deeply, you can look at the transcript from a talk given by E.M. Purcell on this very subject.

Or the Youtube video demonstrating the reversibility of flows in Low reynolds number fluids and several other demonstrations.

Sep. 16 2015 07:39 PM
APL from Toronto, Canada

Actually the relative sizes are way off in your description. An average water molecule has a diameter of about 2.75 Angstroms (that's 2.75 x 10-10 meters for those who remember a little of their high school science). An average human sperm has a head that is about 5 microns in size (that's about 5 x 10-6 meters). The sperm is therefore about 18200 times bigger than a water molecule, so yeah it's harder to plow through the water than if it was a sperm whale, but it's still not "equal sized H2O thingies". Compared to a human it would be like like moving through walnut sized "thingies".

Nov. 20 2013 04:17 PM
Fred Land from Fort Worth, Texas

This reminds me of a performance by Laurie Anderson in the early 80s.

Oct. 10 2013 08:47 AM
Toni from Princeton, NJ

A small comment for the illustrator. Cows have four teats not six. Goats have two. Nonsensical perhaps since cows have singlets and goats bear multiples, but there it is.
Very disturbing, on the level of watching a car ride upside down on the water's surface.
You would understand if you had been face to teat with as many udders as I have.

Oct. 09 2013 09:59 AM

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