Surface tension problem

  • #1
1. A small drop of fat floats on the surface of a liquid whose surface tension is s. Surface fat tension at the air-fat interface is s1, at the fat-liquid interface is s2. Determine the thickness of the drop if its radius is r.


2. ##F=\sigma l##
##\delta P=\sigma (\frac 1 R_1 + \frac 1 R_2)##


3. It is well known that a droplet of grease will have a "seed" shape if floating freely on water. I imaginary cut the seed in two, each half has it's contact angle, and I determined it using the fact that surface forces are in equilibrium.
##\sigma = \sigma_1 \cos\alpha_1 + \sigma_2 \cos\alpha_2##
##\sigma_1 \sin\alpha_1 =\sigma_2 \sin\alpha_2##
If I solve this system I get
##\cos\alpha_1=\frac {\sigma^2 +\sigma_1^2 -\sigma_2^2} {2 \sigma \sigma_1}##
I cannot figure out what to do next
 
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