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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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PvtDeth t1_j0m8qdk wrote

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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wattnurt t1_j0lw6y4 wrote

>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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Wrangler444 t1_j0nf7us wrote

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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