Why does wetting fingers help you grab/separate plastic?
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It’s not friction that’s at work here, it’s a property called adhesion, which is the property of certain substances to be more attracted to the molecules of other substances.
Water molecules have more of a tendency to “stick” to the molecules of other substances than to their own.
(The property of molecules of a substance being more attracted to their own kind than those of another substance is known as cohesion.)
That’s why it’s easier to open a plastic bag with wet fingers. The water molecules of the water on your fingers “stick” to those of the plastic bag and allow you to pry it open easily. It’s adhesion.
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