Monday, August 23, 2010

Can elephants fly?

This week BIPH3001 is reading Life in the slow lane: The Low Reynolds-Number World,

chapter 5 in Biological Physics: Energy, Information, Life, by Phil Nelson.

He begins with the following great quote

Nobody is silly enough to think that an elephant will only fall under gravity if its genes tell it to do so, but the same underlying error can easily be made in less obvious circumstances. So [we must] distinguish between how much behavior, and what part, has a genetic origin, and how much comes solely because an organism lives in the physical universe and is therefore bound by physical laws.

– Ian Stewart, Life’s Other Secret

As with each chapter Nelson begins with a Biological question and a Physical idea:

Biological question: Why do bacteria swim differently from fish?

Physical idea: The equations of motion appropriate to the nanoworld behave differently under time reversal from those of the macroworld.

Figure 5.1 is a picture showing the peculiar character of laminar flow characteristic of a Reynolds number less than one. A really cool video of the same experiment is here.

I also enjoyed a video on Reynolds Number from Sixty Symbols which includes the image above of vortex-antivortex pairs created after a volcano eruption, taken by NASA.

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