This is a total tangent but I can't resist: "it's like blowing up a balloon -- as it gets bigger, there's more back-pressure so it gets harder to fill up the l

This is a total tangent but I can't resist: "it's like blowing up a balloon -- as it gets bigger, there's more back-pressure so it gets harder to fill up the last bit." That's not actually the case with a balloon. :) If you think about it I'm sure you've noticed that you have to blow the hardest right when you start, and then it gets easier. The reason has to do with the curvature of the balloon and the fact that the same amount of air causes less and less stretching of the material as it fills up.