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Re: [ProgSoc] Physicists have 'solved' mystery of levitation



Yen Lim wrote:
> I just had to scream to someone..OMG!!!

This is pretty cool. The article mentions that geckos' feet use a
similar force to stick to walls. This is pretty astonishing. Here are
some gecko facts*:

 * Gecko feet are equipped with hundreds of thousands of tiny bristly
hairs (setae), each of which is covered with hundreds of still tinier
bristles (spatulae), each around 200 nanometers long and wide. So we're
talking about a significant amount of surface area.

 * Gecko feet actually rely on the Van der Waals force, not the Casimir
force (the one mentioned in the levitation article). Van der Waals force
is the slight attraction at the molecular level between charged
particles. It only works at very small distances, but the spatulae get
close enough to a surface to take advantage of them.

 * Although gecko feet make use of the Van der Waals force (a variation
of the Casimir effect), they also make use of capillary force to some
as-yet-undetermined degree.

 * Capillary force: even though gecko feet themselves are dry, there is
a thin film of moisture coating all surfaces. The more hydrophilic
(having a tendency to bond with water) a surface is, the better gecko
feet stick. Capillary force is the force seen when using paper towel to
soak up moisture.

 * Gecko feet don't get dirty because particles of dirt are too small to
be held by the Van der Waals force exerted by the small number of
spatulae with which they are in contact. This means they're effectively
self-cleaning.

 * Geckos can't stick to Teflon.

 * Gecko feet are sticky enough to lift most people's weight, but this
would be pretty tough on the gecko.

 * Geckos are a readily-available and safe-to-eat food in "nethack".

In conclusion, geckos are cool, and I want my gecko-foot-mimicking boots.

- Nicholas

References:
http://www.eurekalert.org/pub_releases/2005-11/m-hfs110905.php
http://www.sciencentral.com/articles/view.php3?article_id=218392449
(cool pics)
http://en.wikipedia.org/wiki/Gecko
http://en.wikipedia.org/wiki/Capillarity

(* Well, "facts". They are culled from the Internet.)


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