I am trying to predict the radius of a bubble at 0.4 m deep in a liquid. I know: the surface tension of the liquid (T) .002239 kg*m the pressure outside the bubble at .5 meters depth (Po1) 394.5 kg/m^2 the pressure inside the bubble at .5 meters depth (PI1) 394.723314 kg/m^2 the radius of the bubble at .5 meters depth (R1) .001 m the pressure outside the bubble at .4 meters depth (Po2) 315.6 kg/m^2 I do not know: the pressure inside the bubble at .4 meters depth (PI2) the radius of the bubble at .4 meters depth (R2) What I tried to do was: a two-variable equation, using PI1*(R1^3)=PI2*(R2^3) (p1v1=p2v2) and R2=2T/(PI2-Po2) (http://hyperphysics.phy-astr.gsu.edu/hbase/surten2.html) I solved it and eventually got: -Po2(R2^3)-2T(R2^2)+(PI1*(R1^3)=0 However, when I solved the equation I got a negative number, while I'd expect it to be a little bit bigger than a millimeter... I checked my math a few times and I'm pretty sure the equations I'm using make sense?? Does anyone know what's wrong??