Life’s Devices

“Teresa Nielsen Hayden”:http://nielsenhayden.com/electrolite/ links to a “terrific paper”:http://brodylab.eng.uci.edu/~jpbrody/reynolds/lowpurcell.html by E.M. Purcell called “Life at Low Reynolds Number.” The Reynolds Number is, roughly, the ratio of intertia to viscosity in fluids, and if you want to learn more about it I strongly urge you to read the rest of the talk for yourself. I learned about the Reynolds Number in graduate school. It’s not something they teach sociologists, as a rule, but I discovered during my first year that Princeton University Press often had sales at the University Store. Because I am in inveterate dilettante — er, I mean, polymath — I picked up a great book by “Steven Vogel”:http://fds.duke.edu/db/aas/Biology/faculty/svogel called “Life’s Devices”:http://www.amazon.com/exec/obidos/ASIN/0691024189/kieranhealysw-20/ref=nosim/.

It’s a course in biomechanics, the subject at the intersection of biology, physics and engineering. But it’s also a great read. It’s terrifically well-written. Don’t worry if you (like me) haven’t had anything in the way of physics since the early years of high school. Vogel is sympathetic, noting that biologists themselves are often essentially in this position,

bq. except that most of us were subjected to a few college courses in physics and mathematics, so we can’t easily admit either innocence or fear. As James Thurber said about the founding editor of _The New Yorker_, “Ross approached things mechanical, to reach for a simile, like Henry James approaching Brigitte Bardot. There was awe in it, and embarrassment, and helplesslness.”

Here’s an excerpt, courtesy of Amazon, from a section about insects and other creatures that have the ability to walk on water. Vogel says

It’s no trick at all to concoct a dimensionless index to the practicality of standing or walking (not floating or swimming) on the surface of water, held up by the force of surface tension on from hydrophobic (nonwettable) foot. All that is needed is the ratio of the force holdin gthe creature up to that pulling it down. The upward force is simply the surface tension γ … times the length of the air-water-foot contact line (usually the combined perimeter of the feet). The downward force is gravitational, the usual _F = mg_ or approximately the density (of the organism) times length cubed times gravity. We get, then, as an index (call it Je, the Jesus number):

… With that mild bit of sacrilege (apologies to the offended), we have probably plumbed enough of these indices to persuade any skeptic that discrete dimensions are no prerequisite for applicability to the physical world.

Great stuff. I think you should do yourself a favor and “buy it”:http://www.amazon.com/exec/obidos/ASIN/0691024189/kieranhealysw-20/.