Editing Surface tension (section)

===Liquid surface===
[[Image:Površinska napetost milnica.jpg|thumb|Minimal surface]]
To find the shape of the [[minimal surface]] bounded by some arbitrary shaped frame using strictly mathematical means can be a daunting task. Yet by fashioning the frame out of wire and dipping it in soap-solution, a locally minimal surface will appear in the resulting soap-film within seconds.<ref name="s_z"/><ref>Aaronson, Scott (March 2005) [https://arxiv.org/abs/quant-ph/0502072 NP-complete Problems and Physical Reality] {{Webarchive|url=https://web.archive.org/web/20180223065653/https://arxiv.org/abs/quant-ph/0502072 |date=2018-02-23 }}. ''ACM SIGACT News''</ref>

The reason for this is that the pressure difference across a fluid interface is proportional to the [[mean curvature]], as seen in the [[Young–Laplace equation]]. For an open soap film, the pressure difference is zero, hence the mean curvature is zero, and minimal surfaces have the property of zero mean curvature.