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

Explanation:

• In bubble, the force due to excess pressure inside the bubble acts upward whereas the force due to surface tension acts downwards even though it is tangential.
• Hence the force due to excess air pressure is balanced by the force due to surface tension.
• The perpendicular force is due to difference between the air pressure inside and outside the bubble.  
• This difference between the air pressures depends on the surface tension.
• The air pressure inside the bubble is always greater than the air pressure outside the bubble to maintain the spherical shape.

Answer 2

It has no component perpendicular to the horizontal surface. As a result, there is no pressure difference between the liquid side and the vapour side. ... Thus, there is always an excess of pressure on the concave side of a curved liquid surface over the pressure on its convex side due to surface tension.