• Liquid droplets behave like small
balloons filled with the liquid on a solid
surface, and the surface of the liquid
acts like a stretched elastic membrane
under tension.
• The pulling force that causes this
tension acts parallel to the surface and
is due to the attractive forces between
the molecules of the liquid.
• The magnitude of this force per unit
length is called surface tension (or
coefficient of surface tension) and is
usually expressed in the unit N/m.
• This effect is also called surface
energy [per unit area] and is expressed
in the equivalent unit of N m/m2.