How do geckos defy gravity? - Eleanor Nelsen
-
0:07 - 0:10It's midnight and all is still,
-
0:10 - 0:15except for the soft skittering
of a gecko hunting a spider. -
0:15 - 0:17Geckos seem to defy gravity,
-
0:17 - 0:18scaling vertical surfaces
-
0:18 - 0:20and walking upside down
without claws, -
0:20 - 0:24adhesive glues or super-powered spiderwebs.
-
0:24 - 0:27Instead, they take advantage
of a simple principle: -
0:27 - 0:31that positive
and negative charges attract. -
0:31 - 0:34That attraction binds together
compounds, like table salt, -
0:34 - 0:37which is made of positively
charged sodium ions -
0:37 - 0:40stuck to negatively charged chloride ions.
-
0:40 - 0:42But a gecko's feet aren't charged
-
0:42 - 0:45and neither are the surfaces
they're walking on. -
0:45 - 0:47So, what makes them stick?
-
0:47 - 0:51The answer lies in a clever combination
of intermolecular forces -
0:51 - 0:53and stuctural engineering.
-
0:53 - 0:58All the elements in the periodic table
have a different affinity for electrons. -
0:58 - 1:03Elements like oxygen and fluorine
really, really want electrons, -
1:03 - 1:07while elements like hydrogen and lithium
don't attract them as strongly. -
1:07 - 1:14An atom's relative greed for electrons
is called its electronegativity. -
1:14 - 1:16Electrons are moving around all the time
-
1:16 - 1:20and can easily relocate
to wherever they're wanted most. -
1:20 - 1:24So when there are atoms with different
electronegativities in the same molecule, -
1:24 - 1:26the molecules cloud of electrons
-
1:26 - 1:30gets pulled towards
the more electronegative atom. -
1:30 - 1:33That creates a thin spot
in the electron cloud -
1:33 - 1:36where positive charge
from the atomic nuclei shines through, -
1:36 - 1:41as well as a negatively charged
lump of electrons somewhere else. -
1:41 - 1:43So the molecule itself isn't charged,
-
1:43 - 1:48but it does have positively
and negatively charged patches. -
1:48 - 1:52These patchy charges can attract
neighboring molecules to each other. -
1:52 - 1:54They'll line up so that
the positive spots on one -
1:54 - 1:58are next to the negative
spots on the other. -
1:58 - 2:01There doesn't even have to be a strongly
electronegative atom -
2:01 - 2:03to create these attractive forces.
-
2:03 - 2:05Electrons are always on the move,
-
2:05 - 2:08and sometimes they pile up
temporarily in one spot. -
2:08 - 2:12That flicker of charge is enough
to attract molecules to each other. -
2:12 - 2:15Such interactions between
uncharged molecules -
2:15 - 2:18are called van der Waals forces.
-
2:18 - 2:21They're not as strong as the interactions
between charged particles, -
2:21 - 2:25but if you have enough of them,
they can really add up. -
2:25 - 2:27That's the gecko's secret.
-
2:27 - 2:30Gecko toes are padded
with flexible ridges. -
2:30 - 2:33Those ridges are covered
in tiny hair-like structures, -
2:33 - 2:37much thinner than human hair,
called setae. -
2:37 - 2:43And each of the setae is covered
in even tinier bristles called spatulae. -
2:43 - 2:47Their tiny spatula-like shape is perfect
for what the gecko needs them to do: -
2:47 - 2:51stick and release on command.
-
2:51 - 2:54When the gecko unfurls its flexible toes
onto the ceiling, -
2:54 - 2:59the spatulae hit at the perfect angle
for the van der Waals force to engage. -
2:59 - 3:01The spatulae flatten,
-
3:01 - 3:03creating lots of surface area
for their positively -
3:03 - 3:08and negatively charged patches to find
complimentary patches on the ceiling. -
3:08 - 3:14Each spatula only contributes a minuscule
amount of that van der Waals stickiness. -
3:14 - 3:17But a gecko has about two billion of them,
-
3:17 - 3:20creating enough combined force
to support its weight. -
3:20 - 3:26In fact, the whole gecko could dangle
from a single one of its toes. -
3:26 - 3:28That super stickiness
can be broken, though, -
3:28 - 3:31by changing the angle just a little bit.
-
3:31 - 3:34So, the gecko can peel its foot back off,
-
3:34 - 3:38scurrying towards a meal
or away from a predator. -
3:38 - 3:42This strategy, using a forest
of specially shaped bristles -
3:42 - 3:46to maximize the van der Waals forces
between ordinary molecules -
3:46 - 3:48has inspired man-made materials
-
3:48 - 3:52designed to imitate
the gecko's amazing adhesive ability. -
3:52 - 3:56Artificial versions aren't as strong
as gecko toes quite yet, -
3:56 - 3:58but they're good enough to allow
a full-grown man -
3:58 - 4:02to climb 25 feet up a glass wall.
-
4:02 - 4:07In fact, our gecko's prey is also using
van der Waals forces -
4:07 - 4:09to stick to the ceiling.
-
4:09 - 4:14So, the gecko peels up its toes
and the chase is back on.
- Title:
- How do geckos defy gravity? - Eleanor Nelsen
- Description:
-
View full lesson: http://ed.ted.com/lessons/how-do-geckos-defy-gravity-eleanor-nelsen
Geckos aren’t covered in adhesives or hooks or suction cups, and yet they can effortlessly scale vertical walls and hang from ceilings. What’s going on? Eleanor Nelsen explains how geckos’ phenomenal feet allow them to defy gravity.
Lesson by Eleanor Nelsen, animation by Marie-Louise Højer Jensen.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 04:30
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