> When you blow up a balloon, the volume of rubber remains the same, but the area gets larger-- because it expands into open space. Well, actually you're consi

> When you blow up a balloon, the volume of rubber remains the same, but the area gets larger-- because it expands into open space. Well, actually you're considering the air there - so it doesn't work. Ignore the air and think about how the balloon skin moves through the medium. In fact the balloon can be considered as not expanding into open air; simply more air is inside it than before - equally a little less air is outside it than there was before (ignoring pressure differences for the moment). Imagine if the skin was perfectly flat and was stretched. The air "moves" around it but is irrelevant to the expansion (and thinning) of the skin. The example only demonstrates how an object can have a larger area without changing volume. Same principle - but in the balloon it is easier to demonstrate relative movement. Im only basing this on my own experience but anyone I've ever given the proper explanation too has gone "oh yeh, I see" (or something the that effect).