Normal stress balance on a translating bubble
= Normal stress balance on a translating bubble
The dipolar normal <traction> is balanced by buoyant <hydrostatic pressure> and the concentration-dependent normal capillary stress, in addition to the constant gas pressure and equilibrium Laplace pressure. A degree-one shape perturbation translates a sphere rather than deforming it; the balance fixes the terminal speed. A uniform gas pressure alone cannot balance this mode.