Take the 2-minute tour ×  How do you explain point 44 of the
attached pdf document on surface tension? Here's the link.  How
is the direction of surface tension 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 the forces on liquid? Any help will be appreciated.
share|improve this question add comment  1 Answer  up vote 5
down vote accepted  The problem is azimuthally-symmetric, so the
tangential direction is the one with no azimuthal component,
i.e. the one "straight up the side" if you were a small mountain
climber climbing from the surface to the top of the drop.  All
three surface tensions are required because all three exert
forces. For example, if the solid-air surface tension were
extremely high, the system would try to minimize the area of
contact between the surface and the air, which corresponds to
spreading the drop out flat. If the solid-air surface tension
were very low, the opposite would occu