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
In the case of the car, the water acts as a lubricant – it gets in between the tire and the road surface and allows them to move over each other more freely by preventing them from getting close enough together that the rough surfaces of the road and tire rub against each other. In the case of turning a page, the water sticks to your skin and the fibres of the paper by adhesion – the water molecules are very slightly attracted to the paper and to your skin, and then cohesion, the force between the water molecules themselves, holds the water together so that when you move your finger, you pull on the water, and the water pulls on the paper, and so the paper sticks to your finger.
In the case of the car, the water acts as a lubricant – it gets in between the tire and the road surface and allows them to move over each other more freely by preventing them from getting close enough together that the rough surfaces of the road and tire rub against each other. In the case of turning a page, the water sticks to your skin and the fibres of the paper by adhesion – the water molecules are very slightly attracted to the paper and to your skin, and then cohesion, the force between the water molecules themselves, holds the water together so that when you move your finger, you pull on the water, and the water pulls on the paper, and so the paper sticks to your finger.
It depends on the thickness of the layer of water and the surfaces involved. In the case of paper, the water wants to soak both into the paper And your skin but there’s not enough water to do both. So the water compromises and tries to stick to both.
In the case of car tires and roads there’s more than enough water to keep the two separate and the water doesn’t want to soak into the rubber tires or oily asphalt (they use some super thick petroleum byproducts to make asphault) and tries to repell them both. If there’s enough water and the car is moving fast enough this can cause the car to “surf” on a thin layer of tire-repelling water. This is known as Hydroplanning and it can lead to a Very Bad Day.
It depends on the thickness of the layer of water and the surfaces involved. In the case of paper, the water wants to soak both into the paper And your skin but there’s not enough water to do both. So the water compromises and tries to stick to both.
In the case of car tires and roads there’s more than enough water to keep the two separate and the water doesn’t want to soak into the rubber tires or oily asphalt (they use some super thick petroleum byproducts to make asphault) and tries to repell them both. If there’s enough water and the car is moving fast enough this can cause the car to “surf” on a thin layer of tire-repelling water. This is known as Hydroplanning and it can lead to a Very Bad Day.
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.
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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