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Cut a narrow slit in a thin sheet of opaque material. Immerse the sheet in a liquid, such as water. After removing the sheet from the liquid, you will see a liquid film in the slit. The question is: why does water make a liquid film and not stay where it was originally?

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Perhaps you should consider this in the light of your other question. I get the feeling that you are studying the subject for the first time, so I will suggest that these questions may be related. Also, may I direct you to our advice on asking basic questions so that we will answer them? –  dmckee Nov 15 '12 at 21:32
    
I agree with dmckee that the questions are related. I am giving you a +1 to the question so you can have points and be able to comment. –  anna v Nov 16 '12 at 4:58
    
Related question by OP: physics.stackexchange.com/q/44304/2451 –  Qmechanic Nov 23 '12 at 22:22
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Molecules of water (H2O) are polar, they are small electric dipoles. In the interior of a volume of some liquid water (pure), the molecules can arrange themselves to minimize the electric fields. At a surface or edge of the volume the fields would have to be un-accommodated or interacting with the material with the slit. Sounds like one pole or the other is attracted to the material and the slit is sufficiently narrow that molecules can form bridges across.

Solutes dissolved in the water could change what you observe.

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