h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

When I was in Lanzarote on my holidays, I bought a lovely wall hanging of a lizard. It is made from flat metal painted blue and cut out in the shape of a lizard. They're very common around Lanzarote, and I intend to hang it outside in my "Mediterranean Corner", which was a rather dull, white corner of the side passage which we're brightening up with climbing plants in a pot.

I see now that the lizard is actually a gecko, as it has those splayed toes with circular pads for sticking to walls.

I've heard a theory that geckos use Van der Waals force, a strange inter-atomic force, to stick to walls, as they can stick to just about anything, including glass. I know that this isn't fully accepted. My personal theory is that they use suction on smooth surfaces.

This should be easy enough to test. All we need is a glass tank, a vacuum pump, a gecko and a tiny space-suit-helmet connected to air tanks on the gecko's back. We can pump all the air out of the glass tank and see does the gecko still stick to the wall, even in vacuum. That will prove conclusively whether it is suction or not.

I can perhaps help with the air tank portion, I think I still have a couple of very small cylinders for a dual-tank torch that I bought in the '80s. The cylinders are only about 2.75" long ... Not sure what you could find for a regulator though, lest the poor beastie instantly become an unhappy balloon.

*wonders whether Gnomon smuggled my Gecko home with him*

They're certainly amazing creatures, but I've not seen mine now for ages. I think he's left me.

For technical advice of any description you only need to ask the crew here: http://wsogmm.h2g2.com/dna/h2g2/alabaster/F19585?thread=2337043&latest=1

That's a good conversation. There's some seriously steampunk chappies over there.

my friend has a pet Gecko - should we ask her to help out with this experiment?

Do suction pads not work in a vacuum, then? What has air pressure to do with the attachment?

We'll need to build the breathing helmet, first. What colour do you think the gecko would prefer?

Suction pads work by air pressure pushing on the pads.

I would guess that if there is an absence of air under, and normal air pressure outside, the 'cup' is pushed to the surface by air pressure. Though I am sure Gnomon can be far more correct in details ...

That'll learn me for pausing before posting ...

I think red or royal blue. Although red doesn't really go with bright green.

Let's go for burnt orange? with flames on it. I'm sure he'd feel so cool with that...

Can we have him skate around on an air hockey table, too?

but he'd stick to the parts where the holes aren't blowing!!

Teeny dabs of silicon grease, and he'd skate easily everywhere!

But might defeat the vacuum chamber experiment, with the go-fast flamey helmut. So best keep the hockey games for later relaxings.

the friend with the gecko said he'd prefer a black helmet with flames...

and if possible a little superhero suit with pants on the outside...

I don't think she's taking this seriously enough.

I believe this experiment has already been done:

Dellit, W.-D. 1934. Zur anatomie und physiologie der Geckozehe. Jena. Z. Naturw, 68613-656.


From http://icb.oxfordjournals.org/content/42/6/1081.full#ref-18

"Mechanisms of adhesion in Geckos"

The idea that the individual setae acted as miniature suction cups was first debated in the insect adhesion literature (Blackwall, 1845; Hepworth, 1854), but was later proposed for gekkonid lizards by Simmermacher (1884). However, there are no data to support suction as an adhesive mechanism, and the adhesion experiments carried out in a vacuum by Dellit (1934) suggest that suction is not involved. Furthermore, our measurements of 10 atm of adhesion pressure (Autumn et al., 2000) strongly contradict the suction hypothesis.



Zube

I still think the theory should be tested, with a go-fast helmut and speedy super-hero garb ... That would be one variant that probably has not been done before.

Thanks Zube. So they know it's not suction but are not clear what it is.

Cancel the order for the mini gecko helmets.

Well, they say more interesting work is needed, but think Van der Waals force is strongly supported by their experiments:

"Since van der Waals force is the only mechanism that can cause hydrophobic surfaces to adhere in air (Israelachvili, 1992), the GaAs and hydrophobic MEMS semiconductor experiments provide direct evidence that van der Waals force is the mechanism of adhesion in gecko setae, and that water-based capillary forces are not significant."