What does it mean for a bubble to be in equilibrium?

[Matthollyw00d]

What does it mean for a bubble to be in equilibrium?
I assumed it just meant that the forces expanding it and the forces compressing it were equal, hence it was at a steady radius. Is there more to it than that?
I'm working on an EM problem so I don't think the specifics are important, I just need some general knowledge on bubbles (and I have none, besides common intuition). Any information pertaining to surface tension would be the most relevant.
Thanks.

 

[cragar]

Prof. Julius Sumner miller has a cool video on soap bubbles .

 

[Studiot]

Are you referring to bubbles of gas in a liquid, and if so from dissolved gas those formed when the liquid boils.

or

Are you referring to soap bubbles in air?

 

[Matthollyw00d]

Interesting video. Not really helpful, but interesting none-the-less.
EDIT:
Soap bubbles

 

[Studiot]

OK

The pressure inside the soap bubble is greater that the pressure outside.

The difference is balanced by a ring or circumferential force acting in the soap film due to the surface tension.

The mechanics is similar to the droplet one I gave in post#8 of this thread

https://www.physicsforums.com/showthread.php?t=384725&highlight=surface+tension&page=2

go well

 

[Matthollyw00d]

OK. So we have a soap bubble, with P_0 outside the bubble \gamma for a surface tension on the bubble. So the Pressure inside denoted
P_A:=\frac{4\gamma}{R}+P_0.
Now if that bubble expands say to a radius, S for whatever reason, does P_A remain constant inside, to give me a set of equations? Or does the
F_A:=P_A(4 \pi R^2) remain constant and the P_A adjust for the changing radius?

 

[RandomGuy88]

Prof. Julius Sumner miller has a cool video on soap bubbles .

This guy is my hero!

I wish I had a teacher that was this exciting!

 

[cragar]

Ya Julius is pretty amazing ,