Why is Force of Bubble Given by 2(2πR)σs?

[werson tan]

Homework Statement

why the force of bubble is given by the formula of 2(2 pi R ) σs ? why not (2 pi R ) σs + (2 pi R+ ΔR) σs ? Since the radius of th outer circumfernece and inner circumference are the different ?

Homework Equations

The Attempt at a Solution

 

[haruspex]

Because for most purposes the difference is too small to worry about. The thickness of the bubble wall is usually far smaller than the radius of the bubble.

 

[werson tan]

Because for most purposes the difference is too small to worry about. The thickness of the bubble wall is usually far smaller than the radius of the bubble.

i have one more question here . I was also told that the pressure at the concave side of the bubbles is higher ... why is it so ? is it because of the circumference of the pressure at the concave side is higher?