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goatharper t1_j0knvyk wrote

They stick to walls using many little points of contact. Any one point of contact will not hold them; they need many. So to let go, they just "unstick" one point of contact at a time until their little hands (or feet) don't have enough points of contact to stay stuck.

It's a delicate little dance they do with their muscles, but of course they do it without even thinking about it, just as you manage to stay upright on two feet without thinking about it. Took you a while to learn to do that.

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0xB0BAFE77 t1_j0l6byv wrote

Funny story about geckos and VDW forces...

In 2014, a study by Hadi Izadi, Katherine Stewart, and Alexander Penlidis determined that van der Waal's force isn't the primary cause of a gecko's ability to stick to things. Instead, it's a phenomenon called contact electrification-driven (CE-driven) electrostatic interaction.
Dellit, the scientist who originally did a lot of studies on geckos and who is referenced quite often when dealing with them, dismissed CE-driven electrostatic interactions as being the reason geckos can stick to things.
The linked paper goes on to explain the flaws in Dellit's testing methods and why CE worked even after Dellit tried to eliminate it.

It should be noted that van der Waals force does play a part in the gecko's abilty to stick to things but it's not the true reason a gecko can stick to almost any surface.

Regardless of the technical reason behind the ability to stick, the setae (see-tee) on its feet are what are responsible for being able to stick and unstick. And when a gecko wants to let go, it does so the same way we remove a strong magnet from something. We pull up at one point and break the magnetic bond.
If you have a strong magnet on a fridge, you don't just grab it and pull it straight back. You pry it from one corner (usually sliding it off the edge of the fridge so you can pull up on one edge).
Geckos do the same thing. When they want to let go, they angle their setae away from the surface and this breaks the grip/attraction.
It doesn't pull its foot straight back all at once. It slightly twists, breaking contact at an edge where the force is weakest.

Edit: Typos and clarified a couple sentences.

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mckulty t1_j0lnmdn wrote

Replying to dolfijntje (#952,564)

Learning to peel their feet off is a simple coordination programmed in reflex arcs at the spinal cord and probably already developing at hatch-time.

Standing and walking for humans involves the ears and cerebellum and higher functions that take a lot longer to develop.

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DeaddyRuxpin t1_j0lochd wrote

Replying to mckulty (#954,397)

So it’s really very much like humans gripping something. Infants at birth already know how to curl their hand to wrap fingers around an object and grip it. No one had to teach us how to do that and our own learning just refined the process to make it more effective. The core grip coordination knowledge was already present at birth.

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mattsslug t1_j0ltnhn wrote

Replying to Foxs-In-A-Trenchcoat (#952,776)

Yup, I have a crested gecko, watching how he releases is quite interesting.

The way his toes curl backwards to release.

He can be stuck to the glass all day sleeping upside down with zero effort, then when he wants to move he just curls those toes and off he goes, it's all so effortless.

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wattnurt t1_j0lw6y4 wrote

Replying to 0xB0BAFE77 (#953,349)

>If you have a strong magnet on a fridge, you don't just grab it and pull it straight back. You pry it from one corner (usually sliding it off the edge of the fridge so you can pull up on one edge).

Slight correction, that's not really the reason for moving a magnet sideways for removing it, I.e. it's not because of mechanical leverage like you suggest. While the total amount of energy is of course the same no matter how you remove the magnet, the way the magnetic field lines run it is simply easier to impart that energy by sliding it sideways instead of pulling it straight up.

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PvtDeth t1_j0m8qdk wrote

Replying to 0xB0BAFE77 (#953,349)

I once found a gecko that had died while it was on the side of a metal pole. From it's dehydration,you could tell it had been dead for at least half a day. I took it off to get rid of it and it was still stuck really well. It felt like peeling Velcro.

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Wrangler444 t1_j0nf7us wrote

Replying to wattnurt (#954,878)

Nah, definitely works like a lever. Put a pull retrieval magnet flat on a metal plane and pull straight back on a rope, then lift it by levering, no contest. W = f x d. Many times the force will be required to pull straight back from the middle

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ZZ9_Plural t1_j0nx8bi wrote

Shear adhesion makes use of microstructures to activate adhesive forces between a surface and the gecko's toes when shear force is applied in a certain direction. That's force applied in parallel direction to the surface. Removing shear or pushing in the opposite direction will deactivate the adhesion. I'm only getting this info from an engineering paper by Hawkes et al. about gripper design, so it may be a bit different with geckos.

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SmallTestAcount t1_j0sqjey wrote

Van der waal forces are not very strong, you need a lot of surface area for the effect to be noticeable. If you reduce the surface area the total force will also be reduced. The way a gecko will reduce the surface area is by peeling its feet off instead of pulling on their entire foot. It's similar to how if you want to remove tape you will peel it instead of pulling

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