Why are your hands slippery when dry, get “grippy” when they get a little bit wet, then slippery again if very wet?
In: Physics
The surface tension of water is greater than the surface tension of your dry skin, which is mostly just tiny dead flaky bumps. Once you have too much water, no, you’re no longer dealing with service tension and now you’re dealing with fluid viscosity, which counteracts the tension.
Source: science and 25 years of hyperhidrosis presenting primarily in the hands and feet
Water has a high surface tension. Think of this as water molecules being so attracted to themselves that they minimize the surface area at any water/air interface. This is why water forms into beads or droplets. If you add a little bit of water to your finger and apply it to a plastic grocery bag or book page, when you pull away the top layer of the bag or book page will move with your finger. Separating from your wet finger would require that the water/air surface area increases against the surface tension force which is trying to minimise the area.
If there is enough water to produce a thin film between two sliding surfaces lubrication will occur. Some good examples of this are bearings, air hockey tables, or walking on wet brick. You would only notice this briefly while walking, but the thin layer of water would cause you to slip before your shoes contact the ground.
“There’s a fine line between between ideal friction and ideal lubrication.” – Dr. Ruth Westheimer
van der waals forces, and probably water displaces microscopic air pockets creating a slight suction effect
If you look at your fingers, you’ll see that there are lots of little ridges. If you lick your finger, you create a little area of dampness on the tip of the finger. When you press it onto a surface, you squeeze water out in exactly the same way as if you were squeezing a sucker onto a pane of glass. You get this attraction of the water locking onto the molecules on the surface of the page and locking onto the ridges on your finger and it gives you a bit more grip.
However, when your hands have a huge puddle on it, what you end up with is a very thick layer of water. You have a layer of water coating your hands, a layer of water coating the other thing you are holding and a layer of water between the two. You end up with a layer of water sandwiched between two other layers of water and that it very slippery.
This is exactly the reason why tires on cars have tread. The tread means that your tire squashes the water out through the tread pattern and stops you getting this slippery sandwich and gives you a better grip on the road. Not enough tread and you slip because the pressure is all distributed evenly, a little water and you get a suction type effect, and too much water and the two objects aren’t actually touching each other and you hydroplane.
There are two forces at work here when it comes to wet grip: Surface tension and Friction.
Water molecules want to cling to things. When water is surrounded by water, it clings to the surrounding water. The surface of water, however, can’t cling as much to surrounding water and thus will cling to anything that touches it.
So, if you have a thin layer of water on your hands, the surface tension from the water will cling to things, which will feel a little grippy. But, if you add too much water, the water below the surfaces will cling to itself and become slick.
The stronger force from grip comes from friction. Friction comes from frictional coefficient and force. Water lowers the coefficient of friction, so water will always make grip from friction weaker.
So: Having slightly wet hands will provide grip to things that don’t require force (like opening a plastic bag, which is really pulling the two parts of the bag apart, not gripping them) The surface tension will provide some cling. Too much water, however, and surface tension is negated by the slickness of the water under the surface.
However, any wetness will reduce grip generated by friction, which is our main gripping ability, as we can control friction by pushing harder. So overall the grip “from a little wet” is only useful in certain circumstances, in almost every other case dry hands will aide grip more.
Edit: I missed one thing: skin (and some absorptive fabrics and materials) soften when wet. This leads to a higher coefficient of friction. However, most non absorptive materials, when wet, have a lower coefficient of friction. Additionally, as I stated, too much water acts as a lubricant and lowers friction on most materials. So… It really depends on the materials and how much water there is water will make two materials grippier or slipperier.
You know when your shoes get really really old and the rubber soles are hard like plastic? You try walking on the linoleum floors at school and slip if you’re not too careful? Or when your shoes are caked in mud, you run into the house, then slide on the wood floor and fall on your butt? That’s kind of what’s going on. Your fingers need a regular amount of moisture to work properly and grip stuff. Too much and you lose grip again.
Im sorry if I dont understand this cause I dont have experience with American culture. But ELI5 like these confuse me.
They seem to be asking for explanations on things that aren’t true in the first place.
I mean no offense. But I wonder if the OP can describe what they mean by slippery when dry and gripper when slightly wet. In my experience, any amount of water makes things more slippery, except in circumstances where things like plastic bags stick to water.
“Why can I masturbate dry, or with a ton of water in the shower, but not when my hands are damp?”
This reminds me; if you have slippery hands while riding bmx just rub a little dirt in your hands and your hands will be dry for awhile (close to an hour)
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