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Why does liquid stay in a horizontally turned straw but not in a glass?

What’s the difference between a Glass and a Straw?  Both are cylindrical.  Why does water spill out of one when tipped over and not the other?  Because the glass is bigger you say… but is that all?  Surface tension, hydrogen bonds, and capillary action you say?  Maybe…

New research shows that it is not only the size, but the shape of a tube that determines whether liquid will spill out of it when tipped over.   Geometry changes everything!  This new understanding may seem simple, but actually can be complicated, especially when it comes to the practical applications in technologies that have liquids present on a smaller scale, such as biomedical diagnostics and oil recovery.

Co-author Professor Parry, from the Department of Mathematics at Imperial, said: “If your pint glass falls over, tragedy has struck and you know you’re going to spill your beer. But conversely that doesn’t necessarily happen if you suck your beer into a straw and turn that horizontally. In that case common experience tells us that if the straw is thin enough the liquid stays in. Now, we have discovered that it should be possible to create minute straw shapes that would mean that any liquid spills, or empties out of the tube, no matter how thin it is.”

Check out which geometries and cross sections hold the liquid and which don’t’.

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