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Let's say we have a drop of water on a surface. Its surface tension maintains the shape. But was the water evaporates, the molecules leaving it, leave from the surface. Shouldn't the evaporation disturb the surface tension causing the water droplet to fall apart?

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As the drop gets smaller the ratio of the number of molecules on the boundary compared to those in the main volume gets higher. A smaller drop creates a stronger sphere.

As an exiting molecule leaves the boundary the molecules that were holding it in place lose the outward pull of that molecule and so become pulled only inwards, renewing the contraction of the surface.

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  • $\begingroup$ thank you very much $\endgroup$
    – Rick
    Mar 4, 2020 at 23:30

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