Question

The force of surface tension acts tangentially to the surface whereas the force due to air pressure acts perpendicularly on the surface. How is then the force due to excess pressure inside a bubble balanced by the force due to the surface tension?

Answer 1

The surface of the bubble is curved. The forces perpendicular to the surface has different directions from point to point. The effect of the pressure inside (which is perpendicular to the surface) over an area is to produce a net force tangential to the surface that tries to increase the surface area of the bubble. While the force of the surface tension (acting also tangentially) tries to decrease the area of the bubble. Thus the pressure and the surface tension forces balance each other.