# Direction and magnitude of force due to surface tension

Consider the structure shown above, we know that the force of surface tension acts tangentially to the surface, so the liquid molecules experience force $$F_1$$ which acts tangentially to the liquid surface and the molecules of solid experience force due to surface tension $$F_2$$ which acts tangentially to the solid these two may be same in magnitude but they are not opposite in direction. Hence they do not form action - reaction pair.But , then what should be the action reaction pair for both of them ?

We write the force due to surface tension as F=$$\int Sdl$$ with proper limits with dl as the length separating the two surfaces and perpendicular to the tangent to the surface and S as the surface tension between the two surfaces in contact, consider a small cross-section AB as shown, I’m not able to visualise what should we consider the dl length as, for calculating the force on the AB element.