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Hi! Hope you guys are having a great day! I have a question involving a recent experiment that I performed: What I wanted to do was to see if I could contain water using capillary forces, etc. in a "hollow, rectangular tube" (imagine a regular straw, but then making it into a square- shaped straw, and then elongating two of the sides of that square that are parrallel to each other to create a rectangular-shaped "straw") Anyway, I wasnt able to make the shape perfect due to the materials that I was using to create the shape. But it did seem to work fairly well, althought water did begin to slowly fall out of the tube when it was in the vertical position due to some air bubbles that I thought might of formed when I was taking the entire tube out of the water. The dimensions of the rectangular part of the tube were 0.5cm by about 1in or so, so I dont think the tube was big enought to prevent the capillary forces from keeping the water in. Do you guys have any idea why the water might be dripping out of the tube? Would you guys suggest making the tube more water/air tight or making a perfect recangular shape to prevent trapping air bubbles? Or maybe making it smaller? Any info will help. Thank you guys so much!
Question Date: 2009-11-02
Answer 1:

I don't normally think of capillary action working on the scale of the straw you're using, since I normally think in terms of the tracheids of trees, which are MUCH smaller (I'm a botanist). It could be that the higher pressure when you pull the tube out of the water aids imperfections in causing cavitation, or one thing that occurs to me now is that your tube itself may be flexible and flexing in response to the pressure, again enabling cavitation. I do think a smaller straw would help.

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