Why do we wet a finger to turn pages?

13 June 2013



Here's another question of the week:
When we spill water on a tile floor, we might slip and bash our head, but when we want to turn the page of a book, we lick our fingers to get "traction."
What's going on here?


Chris - You know, a lot of people don't like that finger-licking business with pages because of the potential for... 

Kate - It's the horrible noise!

Chris - Well, that and the germ transmission!

I was thinking about this, why should a wet floor be slippery while a finger that's licked and then applied to a piece of paper should enable you to get a better grip? The wet floor is quite simple to explain, because there you've got a lubricant - a liquid - between the sole of your shoe and the floor. Therefore, the friction will be lower, and therefore, when you push against the floor to try and walk, you're more likely to slip.

But, if you lick your finger, you're putting a film of water over the end of your finger. If you then apply that to the page, you're going to squeeze air out from under your finger between your finger and the page, and the water has a thin film around the edge and is going to prevent the air getting back in, so there's going to be effectively a vacuum - or at least a partial vacuum - between your finger and the page surface, at least for a little while, and that's going to help you get a better grip, I think...


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