1. The problem statement, all variables and given/known data The pressure by the walls of a bubble is 4σ/r (where σ is the surface tension). The radius r of 2 bubbles is measured. After that you bring the two together by connecting them with a straw (the smaller bubble has higher pressure and gets smaller, while the bigger bubble gets bigger). You now measure the new radius of the new bubble. You do this for different values of r_1 and r_2. Find the value of σ. (given atmospheric pressure) 2. Relevant equations p=4σ/r (PV=nRT) (I think) 3. The attempt at a solution Solving the system of equations (PV=nRT for each bubble) The pressure P=p_walls + p_atmosph. You get V by r. T is alway the same (therm. equilibrium) nR adds, when bubbles are fused. Solve for σ. Should I add another relation between the different p_walls? Is this approach ok, or is there something I missed?