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Author Topic: How do geckos RELEASE their grip on a wall?  (Read 4326 times)

Offline John Chapman

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How do geckos RELEASE their grip on a wall?
« on: 25/07/2009 14:57:30 »
Itís fairly well known that the force holding a gecko to the wall is the Van der Waalís force. Each square millimetre of the geckos toe apparently includes around 14,000 minute hairs, each of which is subdivided into up to 1,000 smaller hairs, each of which ends in a microscopic Ďspatulaí to maximise the toeís surface area.

I donít really understand what the Van der Waals force is. At the risk of making myself appear stupid I have to ask: This isnít anything to do with the nuclear forces, is it? Presumably the distances of attraction with the geckoís setae are very much greater. Eh?

The other thing I donít understand is how the gecko releases itís grip. I have just read in an old Scientific American that if a 3oz gecko had every one of itís setae in contact with a surface you could hang about sixth of a ton from it before itís grip failed. For a 3 oz lizard thatís unfeasibly strong! And what happens if one dies in the night? Do you have to get out a crowbar to remove it from the wall? As far as I know you canít switch off the Van der Waalís force so how DOES the gecko let go.
 


 

Offline _Stefan_

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How do geckos RELEASE their grip on a wall?
« Reply #1 on: 25/07/2009 15:39:15 »
They curl their toes upwards, peeling away from the surface. Their toe joints bend in the opposite direction to our finger joints.

Quote
This allows them to overcome the van der Waals force by peeling their toes off surfaces from the tips inward. In essence, this peeling action alters the angle of incidence between millions of individual setae and the surface, reducing the van der Waals force.
http://en.wikipedia.org/wiki/Gecko#Gecko_toes:_setae_and_van_der_Waals_forces
 

Offline John Chapman

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How do geckos RELEASE their grip on a wall?
« Reply #2 on: 25/07/2009 22:08:32 »
Hi Stefan

Yes, I also read that, but after I posted the question. However, the one sixth of a ton (over the four feet) required to release the gecko seems too much to achieve by curling the toes upwards. Have you seen the speed these things move?

Do you have geckos in Australia? Do you know if you can stick one to the wall when it is dead? It would beat fridge magnets!  [8D]
 
« Last Edit: 29/07/2009 07:18:49 by John Chapman »
 

Offline _Stefan_

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How do geckos RELEASE their grip on a wall?
« Reply #3 on: 26/07/2009 05:01:51 »
You could liken the effect to peeling the tab on the lip of a suction cup that's attached to a surface. This curls the lip open just enough to let air rush in and undo the vacuum. In contrast, pulling on the whole cup has little effect.

If you re-read the wiki quote, you will see that the angle at which the setae meet the surface is important. They also start curling from the tips inwards, just like a suction cup.

Robotic geckos with synthetic setae have been made that take advantage of the toe-curling in order to detach their feet.
 

Offline AllenG

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How do geckos RELEASE their grip on a wall?
« Reply #4 on: 26/07/2009 07:32:14 »
Here is a BBC clip about gecko toe curling.
Sir Richard is the narrator.

« Last Edit: 26/07/2009 07:34:37 by AllenG »
 

Offline John Chapman

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How do geckos RELEASE their grip on a wall?
« Reply #5 on: 26/07/2009 08:40:10 »
Thanks stefan and AllenG

That Attenborough clip was fascinating and incredibly relevent. He must have heard me asking the question. It shows in slow motion exactly what you described, stefan.

It also hints at my 'dead gecko' question. He uses skin dissected from a gecko's toes to lift a coin.

Does anybody out there know what happens if a gecko dies while sleeping on a wall? How easy is it to remove without being able to exploit it's toe-curling technique?
 
 

Offline _Stefan_

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Offline John Chapman

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How do geckos RELEASE their grip on a wall?
« Reply #7 on: 26/07/2009 10:27:35 »
That's amazing. How do you all find these links?

This is the picture you linked to:


 
The text says:

How Sticky are a Gecko's Feet?

Turns out sticky enough to continue holding this long dead Gecko on the wall. He has been dead long enough for orange mold or fungus to grow near his tail base and for his eyes to dry out.  He is being held up by his front legs.


I think that's the whole question wrapped up. Job well done! Thanks Stephan.
 
 

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How do geckos RELEASE their grip on a wall?
« Reply #7 on: 26/07/2009 10:27:35 »

 

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