Science Questions

Why do we wet a finger to turn pages?

Thu, 13th Jun 2013

Listen Now    Download as mp3 from the show Extreme Physiology: Everest to Ocean Floor


John Gamel asked:

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 donít like that finger licking business with " alt="" />pages because of the potential forÖ

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 thatís 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, youíve got a lubricant, a liquid between the sole of your shoe and the floor and 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 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 thatís going to help you get a better grip, I think. 


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