When I need to turn a page, water adds a bit more friction making it easier to turn the page. Yet when driving, water reduces friction between wheels and the road.
Why can it do both?
In: 3
Water has two properties relevant here:
– Adhesion
– Cohesion
Adhesion is how well the molecule sticks to other things. Water is pretty adhesive.
Cohesion is how well it sticks to itself. What we is not very cohesive.
So if you get just enough water that there’s only enough to stick to other things, it’s pretty sticky.
But if you have enough water that it forms a thin film, the water-water stickiness can be much lower than the material’s normal friction.
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