We’re all familiar with the problem of pouring a liquid from a narrow-necked bottle. To a certain extent, tilting the bottle further will reduce the time it takes to empty, but if you tilt too far, your smooth pour becomes violent glugging as bubbles forming at the bottle’s mouth block liquid from exiting.
Researchers find that the time it takes to empty a bottle depends both on the qualities of the liquid — its viscosity and surface tension — and on the geometry of the bottle. In particular, they found that the shape of the bottle influences how quickly bubbles grow at the bottle’s mouth when tilted to the critical angle. Their findings suggest that higher tilt angles and faster pours can be achieved by optimizing bottle geometry. (Image and research credit: L. Rohilla and A. Das; via phys.org)