Why does a liquid not spill when you hold down the upper end of a straw while taking it out of a glass? Hoping that is self explanatory. Thanks.
In: Physics
Water has something called “surface tension”- water molecules at the edge of a mass of water hold on to one another more tightly than most liquids, which is why things like leaves and water striders can sit on top of water without sinking- there’s a little skin of water molecules on top of the water.
When you hold your finger at the top of the straw, you are holding back the air from entering the straw, so the water at the top can’t move out of the way. Normally, even with the skin, whole mass of water will slide out like a hot dog out of a hose, but you prevent this by making sure the water at the top stays in place via negative pressure.
This combines with the fact that the water is making a “skin” at the bottom, holding it back, and that makes it so the whole mass of water stays where it is, connected to the sides of the straw with surface tension.
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