# Boyles law question (kind of)

1. May 3, 2012

### DNMock

Trying to wrap my head around this thought experiment and I was hoping to get some expert advice on this:

Take a balloon made out of a rubber that can stretch infinitely thin without breaking blown up to normal balloon size. Next put it in an infinitely large, perfect vacuum and let it go.

If my head is wrapped around this correctly, the balloons radius should expand at a constant rate indefinitely should it not?

2. May 3, 2012

### Andrew Mason

Not unless the balloon material has some magical property that prevents it from providing tension. At some point the pressure inside the balloon will be equal to the inward pressure created by the tension in the rubber and the expansion will stop. This is not a free expansion.

If a gas is allowed to expand freely in a vacuum, the motion of the gas molecules would be random. I don't think the radius of the gas cloud would expand at a constant rate. The radius increase would follow statistical laws for random motion.

AM

3. May 4, 2012

### DNMock

Ah, ok that makes proper sense to me. I felt like it should slow down over time but couldn't figure out why, but it's the tension of the balloon itself. That makes sense now, thank you for helping my head pass it's brain fart :)