| MadSci Network: Physics |
Balloons (like almost all real objects) are not perfectly elastic. It takes more work to blow up a balloon than can be obtained by allowing an inflated one to deflate, because the one that's inflated has lost some of its strength by being stretched.
The second part of the question has a similar answer: the balloon which is inflated has lost some of its elastic strength, so when you squeeze it, it's easier for the air to stretch the already-stretched balloon than to stretch the other balloon.
You can confirm this yourself: blow up a balloon, then let the air out. Now blow it up again. You didn't have to work as hard, did you? When I blow up balloons for my children I will often stretch them with my hands to make them easier to inflate. This works because stretchable material usually loses strength by being stretched.
DJB