If water makes things slippery, why does licking my fingers make it easier to open plastic bags?

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If you’ve ever had trouble opening a plastic groceries bag or bin bag, you can get your fingers wet (with tap water or by licking them) and it’ll make it easier. Why?

In: Chemistry

What makes you think water makes things slippery?

Licking your fingers is taking away the natural oils present there, so there is a less slippery surface to grab the plastic bag with

Different surfaces react to water differently. For example, I have two kinds of concrete in my drive way. One has pebbles and doesn’t get slick. One is smooth and becomes deadly to walk on barefoot when wet.

In addition to removing natural oils, by getting your finger wet, you allow your fingers to make relatively airtight seals against the plastic, and the surface tension of the water will actually make the plastic “want” to adhere to your finger.

However I’d like to point out that in most contexts water is a terrible lubricant. Try having sex in a pool if you don’t believe me.

(Please do not actually try having sex in a pool.)