Why does the friction of a paper towel appear to change from low-high-low depending on it being dry-wet-soaked?

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Why does the friction of a paper towel appear to change from low-high-low depending on it being dry-wet-soaked?

In: Physics

Anonymous 0 Comments

Paper towels are relatively rough. When dry, not much of them is actually touching the surface so the friction is relatively low.

With a little bit of water, the towel becomes much more pliable (more surface contact), the water can bridge from the towel to the surface (even more contact), and the surface tension of the water acting on all those towel fibers gets considerable. All added up, high friction…you’ve basically glued the paper towel to surface using a very thin layer of water.

With a lot of water, the interface is mostly bulk water…the towel isn’t touching the surface much at all and there’s so much water that it’s now acting like a lubricant…it’s not surface tension dominating anymore, it’s (relatively) large volumes of water and now everything is slippery.