Why are your hands slippery when dry, get “grippy” when they get a little bit wet, then slippery again if very wet?

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Why are your hands slippery when dry, get “grippy” when they get a little bit wet, then slippery again if very wet?

In: Physics

24 Answers

Anonymous 0 Comments

When dry, all the “grippiness”, or rather friction, between your hand is skin on the surface’s object.

When just slightly wet, the moisture fills in the tiny gaps between your skin and the object. It basically acts like a weak adhesive.

When your hands are very wet, there is so much water between your skin and the object that it nor just fills in the small gaps mentioned above, but forms a film between your skin and the object, thus greatly reducing grip.

Anonymous 0 Comments

TIL this sub does not explain like I’m 5 anymore. There are a lot of correct answers upvoted most, but none at the top fit the intention of the sub lol.

Anonymous 0 Comments

Is this even true? Is the point of chalk for climbers etc not to dry their hands to increase grip?

Anonymous 0 Comments

Others have explained the sources of this effect: (1) you skin swells and (2) surface tension.

I wanted to add that this is very similar to a story I once read about Albert Einstein musing about beach sand. He noted that it is hard to walk in totally dry sand and also hard to walk in sand that is submerged in water, but easy to walk on sand that is wet but not submerged, right where the waves stop moving up the beach. He then explained his own observation: sand that is wet but not submerged in water sticks together through surface tension.

So this question has an excellent pedigree. I did some googling to find the story and I think this is it, but it is behind a paywall:
[https://physicstoday.scitation.org/doi/full/10.1063/1.2169417](https://physicstoday.scitation.org/doi/full/10.1063/1.2169417)

Anonymous 0 Comments

This is a question of friction. There are two main types of forces contributing to friction.

First we have literal roughness/unevenness in the surface (termed [Asperity](https://en.wikipedia.org/wiki/Asperity_(materials_science))) which means two surfaces can hook into each other, sort of like velcro, and your hands has a lot of these (e.g. finger prints).

The second is a bit less intuitive and is called the Van der Waals force. This can cause friction between smooth surfaces because the force comes from the atoms and molecules themselves. This is the reason you get a better grip on your cellphone case that is made of soft rubber than you get from the glass and hard plastic of the phone itself.

Beyond this it can often be hard to specifically determine what forces will dominate for a given scenario.^([1]) Climbers generally want to chaulk their hands completely dry to get a better grip on the rough surfaces they climb on. If the surface is really smooth then you might want to rely on the Van der Waals force instead, for instance by using indoor running shoes with soft rubber soles when in a gym with equally soft rubber flooring. However, be careful of any lubricant that can come between the smooth surfaces, as this will remove the Van der Waals force completely and make it extremely slippery.

For your specific example I would conjecture that somewhat wet hands strikes a good balance between using the Van der Waals force and the roughness between surfaces to obtain relatively strong friction for a variety of scenarios. Too wet hands could for example act as lubricant on the Van der Waals force. (Dry hands I am less sure of but I have a feeling it could have something to do with reduced surface contact)

>[1] The relationship between frictional interactions and asperity geometry is complex and poorly understood. It has been reported that an increased roughness may under certain circumstances result in weaker frictional interactions while smoother surfaces may in fact exhibit high levels of friction owing to high levels of true contact.” [wikipedia.org/wiki/Asperity](https://en.wikipedia.org/wiki/Asperity_(materials_science))

Anonymous 0 Comments

your hands get grippy when they’re a little bit wet?

Anonymous 0 Comments

Water sticks really well to lots of things, so a little bit of it makes things grippy / sticky, BUT it doesn’t stick to itself nearly so well so too much of it makes things slippy.

Anonymous 0 Comments

No ones hands are “slippery when dry.”

What are you talking about?

We literally chalk our hands before lifting heavy weights or doing bar work to get them as dry and abrasive as possible to maximize friction so we don’t slip.

People this thread are weird

Anonymous 0 Comments

I’ve always said that certain things are slippery when they’re too dry, but also slippery when they’re too wet. A lot of systems on earth balance on the correct amount of water. Slipperiness is no exclusion.

Anonymous 0 Comments

Old ELI5…

Actually, when the ridge on your fingertips and hand get hydrated with water, combined with the crease, will act as a ventouse. Kinda like if you had a thousand of little ventouse on the inside of your palm hand so it stick to slipery surface.