# When we inflate a balloon

1. Apr 16, 2013

### tmv3v

Notice that when we blow up a balloon, or held up a balloon outside a car and accellerate, the balloon doesn't expand constantly. It seems like there is a critical air pressure for the balloon to start expanding. Is that true and how can we calculate this?

Last edited by a moderator: Apr 16, 2013
2. Apr 16, 2013

### mikeph

I'd hazard a guess that the critical pressure for expansion is the atmospheric pressure plus the pressure created from the elastic tension in of the rubber acting to compress the air inside. If you can overcome the sum of these pressures when you blow into the balloon, it will expand.

3. Apr 16, 2013

### Staff: Mentor

The thicker the skin of the ballon of the balloon, the more force it takes to stretch it. But as the balloon expands, its skin gets thinner, so less pressure is required to further expand it. So a balloon is hardest to expand when it's completely uninflated, and once you get it going it keeps getting easier.

4. Apr 17, 2013

### tmv3v

Thank you so much the explaination is so good:)