Is Surface Tension Directed Along or Perpendicular to the Liquid Surface?

[andyrk]

Is the direction of surface tension on the surface of a liquid into the surface or parallel to it along the surface of the liquid? And how? I am confused between both of them because, when we take an example of line on the surface of a liquid, we say that liquid surface is behaving like a stretched membrane with each part (the line has divided the surface into 2 parts) exerting a force parallel to the surface of the liquid or along the surface of the liquid. But when we consider surface tension in terms of molecules, for example, a molecule at the top of the surface is pulled inside due to cohesive attraction from the molecules below it (One more question, is the attraction provided by the molecules below it of gravitational origin, electromagnetic origin or electrostatic origin?) So as the molecule wants to go down surface tension is down the surface perpendicular to it. But it can't be both can it be?

 

[Chestermiller]

Is the direction of surface tension on the surface of a liquid into the surface or parallel to it along the surface of the liquid? And how? I am confused between both of them because, when we take an example of line on the surface of a liquid, we say that liquid surface is behaving like a stretched membrane with each part (the line has divided the surface into 2 parts) exerting a force parallel to the surface of the liquid or along the surface of the liquid.

It's not both. You wrote, "when we take an example of line on the surface of a liquid, we say that liquid surface is behaving like a stretched membrane with each part (the line has divided the surface into 2 parts) exerting a force parallel to the surface of the liquid or along the surface of the liquid." This description is the one that's correct. How this is related to molecular considerations, I don't recall. But you can find the details all worked out in a good book on statistical thermo.

Chet