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Soap bubbles are never "too small" or "too large". What defines the range of possible diameters of a soap bubble?

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Sparkler
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3 Answers3

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I don't know what you define as too large, but soap bubbles can reach very large sizes.

https://www.youtube.com/watch?v=5bjggctu3kw

It's a balance between the surface tension being weak enough to allow the film to stretch to large size but strong enough to not tear as it flexes. The soap added to water is for weakening the surface tension.

Mark H
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At the lower limit, if the bubble is very small the pressure inside will be so large that the gas inside can dissolve into the shell of the bubble, and from there diffuse out to the atmosphere. That limits the life time of small bubbles.

On the large side, huge bubbles (several meters diameter) are certainly possible. These tend to be unstable because they require extremely low surface tension, and thus they don't "keep their shape" very well. Over time they evaporate, or the soap molecules migrate causing an uneven distribution of surface tension along the surface. With insufficient surface tension in some places the bubble will once again burst.

In the absence of evaporation and instability, the ultimate size limit of a bubble may have to do with gravity: the film somehow needs to support the "column of soap bubble" above it, and if you think about hanging a soap film from a thread, you can see that it would be thinner at the top (which is supporting more weight) and thicker at the bottom. There will be a limit beyond which the film cannot support its own weight - I don't know how to compute it.

Floris
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Why soap bubbles have larger sizes than water bubbles?

For the same mass of air m in a water bubble and soap bubble, the soap bubble will have low internal pressure than the pressure in the water bubble. It is because of large diamter and low surface tension. In other words, the effect of an increase in diameter & decrease in surface tension is counterbalanced by decrease in the internal pressure (Pi) of bubble. Po is atmospheric pressure. st is surface tension and d is diameter of bubble. Pi-Po = (8*st) / d

Thanks and have a nice day.

Rohit Kumar
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