Contact angle of liquid drop on solid surface.2

[amk_dbz]

Can anyone explain point 44 of the attached pdf document on surface tension.

(Here's the link in case attachment doesn't work:
http://www.sakshieducation.com/EAMCET/QR/Physics/Jr Phy/12Surface tension _198-208_.pdf

How is the surface tension direction found out?
{i know it tangential but in which direction along the tangent?}
Also why is surface tension for Solid-Air Surface considered when balancing forces on liquid?
Any help will be appreciated
Thank you.

 

[Valerie Park]

Point 44 from the PDF states that the surface tension of a liquid is always directed along the tangential direction of the surface. This means that the force due to surface tension will be in the direction perpendicular to the surface. To determine the direction of the surface tension, it is important to consider the forces acting on the surface. For a liquid-air interface, the forces acting on the surface are the weight of the liquid, the pressure difference between the two sides of the interface, and the surface tension. The direction of the surface tension can be determined by finding the direction in which the sum of all these forces is equal to zero.The surface tension of a solid-air interface is also considered when balancing forces on a liquid because the surface tension of the solid-air interface affects the surface tension of the liquid-air interface. This is because the liquid-air interface is in contact with the solid-air interface and thus, the forces acting on the liquid-air interface are affected by the solid-air interface.