Solving for the pressure difference and then denoting we can rewrite equation (L- 3.1) as
                                            

Contact angle and welting

As shown in fig. a liquid contacts a solid surface. The line at which liquid gas and solid meet is called the contact line. At the contact line the net surface tension depending upon all three materials - liquid, gas, and solid is evident in the contact angle, . A force balance on the contact line yields:

here is the surface tension of the gas-solid interface, is the surface tension of solid-liquid interface, and is the surface tension of liquid-gas interface.