Why Do Balloons Go Bang?
The energy stored in the compressed air inside a balloon is not very large at all. Balloons create very little overpressure, apparently on the order of 5 or 6 mm of mercury when inflated to normal size. On inflation, the pressure must be higher as the rubber just starts to stretch because, from our stress equations above: the modulus (stiffness) of the rubber is initially large, (it then drops off, to finally get VERY large with increasing strain) the balloon wall is initially thick, and the radius of the balloon is small. Pressure falls rapidly as the balloon grows in size. This follows from the stress/pressure relationship, and the stress/strain curve for latex. There is a well-understood differential equation applying to soap bubbles relating surface tension, bubble shape and internal pressure. The surface tension can be thought of as a *constant* hoop and axial stress (NOT a function of strain, as in latex).
