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A boffin at work was trying to bluff his way out of answering a straight question by saying it was too complex to answer. Does anyone know the answer. I know one of you will know.
Question... I hold a standard pub pint glass underwater in a sink of water so it was full of water, no air in glass. I carefully liftd it out of the sink, open end down (upside down), the column of water would be lifted until it broke the surface, then the water would rush out of the glass, as the surface of the water in the glass can't hold the column of water. Ok so far.
I reckoned if the glass diameter was reduced, then at some point the column of water would stay within the column, due to capiliary action or some sort of viscosity/surface tension thing. Does anyone know an equation or a diameter where the water stays in the glass?
(I imagine the answer will be slightly different with different atmospheric pressures, or heights of columns and it will be specific for each fluid).
If the diameter was as small as a biro pen, then it would definately stay in the glass, so the answer is somewhere between 3mm and 100mm.
Any ideas? short of testing it out.
I doubt you'll find an analytical equation for this; surface tension is pretty difficult to define.
You'll have to balance the pressure due to the column (density x height x gravity) against the surface tension/curvature equations ( http://en.wikipedia.org/wiki/Surface_tension)
Erm. Good luck!
cheers. This must be a known equation.
Just wondering if anyone had a refernce to a ball park figure say 7 to 10mm. I know my 15mm pipes can hold water in the (but I suppose they are not all vertical).
Depends on the length - if you take a very long pipe, there will be a massive weight of water pushing against that surface tension at the bottom.
Is that entirely true as the column is not vented? I agree if air could get into the top. Thanks for helping. Thats a good reference to wiki.
Hmm good point, I was being a bit thick. I guess not! It may well just be a function of the tube diameter. Probably also affected by the tube material, temperature, pressure and humidity etc.
I guess its going to have to be a trial and error thing. I'm not clever enough to search beyond google. I wonder if there is a boffin forum, where people answer techy questions (when STW finds itts limit)