# Surface tension and work of a bubble or drop? S

1. Sep 11, 2011

### babybaby

1. The problem statement, all variables and given/known data
While a person breathes in, a typical alveolus expands from a radius of 0.13 x 10-3m to 0.15 x 10-3m. The alveolus behaves as though it has a single surface which is described by
P =2γ/r
ote the following.
The gauge pressure in the alveoli of the lung is denoted Palv.
The gauge pressure just outside the lungs, in the intrapleural space, is P0,which approximates the pressure outside the alveoli.
The average excess pressure in the alveolus, P, while breathing in is 600 Pa, and while breathing out it is 650 Pa.

2. Relevant equations

(a) What is the work done in expanding the alveolus while breathing in?
(b) Use energy transfer ideas to determine the average tension in the alveolus wall while breathing in. Explain your reasoning steps carefully.
(c) In fact P increases while breathing in, by a factor of approximately 1.6. What are the implications of this increase for the tension in the alveolus walls? Be quantitative in your answer.

3. The attempt at a solution
for a im not too sure what to do. cos its a single surface so do we consider it as a droplet? :S and when i try work out using the dE = y dA = y 16 pi r dr P =W = P 4 pi r^2 dr
but if i use y 16 pi r dr it doesnt equal to P 4 pi r^2 dr
whys that? :S
and i dont understand the rest
sorry for the noobness

2. Sep 11, 2011