Why does water make surfaces slippery but help your fingers to grip?
If you spill some water on the kitchen floor, it's obviously very slippery. Yet when you want to turn the pages over in a magazine, you put some water on your hands and it becomes really easy to grip!
It's a very good point. If you look at your fingers, you'll see that there are lots of little ridges. If you lick your finger, you create a little area of dampness on the tip of the finger. When you press it hard onto a surface, you squeeze water out in exactly the same way as if you were squeezing a sucker onto a window. You get this attraction of the water locking onto the molecules on the surface of the page and locking onto the ridges on your finger and it gives you a bit more grip. However, when you've got your kitchen floor with a big puddle on it, what you end up with is a very thick layer of water. You have a layer of water coating your foot, a layer of water coating the floor and a layer of water between the two. You end up with a layer of water sandwiched between two other layers of water and that it very slippery. This is exactly the reason why tyres on cars have tread. The tread means that your tyre squashes the water out through the tread pattern and stops you getting this slippery sandwich and gives you a better grip on the road.