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When we open a tap over a water surface, we get to see a lot of bubbles ("half merged in the water") coming out on the surface.

Now what I saw was that two such nearby half bubbles merge to form a bigger one. But I couldn't really think of what goes on at the point of contact between them. How exactly does air gets transferred from one to the other? Another point which I wanted to mention was that in such mergers, the bigger bubble gets bigger and the smaller one vanishes which is opposite to what I read in my high school about bubble mergers.

So someone please clarify what goes on at the interface.

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  • $\begingroup$ There are two different mechanisms. One is coalescence where the film between the two bubbles bursts, and the other is ripening where air diffuses from the small bubble into the larger one through the film between them. Ripening is usually slow i.e. on a scale of minutes or tens of minutes while coalescence is fast i.e. on a scale of seconds. I would guess you're seeing coalescence, but perhaps you could clarify this. $\endgroup$
    – John Rennie
    Commented May 21 at 8:52
  • $\begingroup$ @JohnRennie Thanks for your comment. Yeah that merging is quite fast (in the order of seconds). $\endgroup$
    – Ankit
    Commented May 21 at 11:18
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    $\begingroup$ I don't know much about ripening but I would guess one contributing factor is probably that smaller air bubbles have a higher internal pressure than larger ones and the merging of two bubbles is a result of pressure balancing to equilibrium. $\endgroup$
    – Hacker
    Commented May 25 at 21:36
  • $\begingroup$ @Hacker Thank you for your comment. Actually I got the answer for the second part (I was thinking it wrongly initially) but what I still don't know is how the air transfer occurs, like is there any opening like thing at the interface or something similar ? $\endgroup$
    – Ankit
    Commented May 26 at 3:01

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