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