The opposite of a bubble – spectrum of science

Amazing physics hides behind many everyday things. felt for many years Hans Joachim Schlichting investigates these phenomena and explains them in his column to the readership of »Scientific Spectrum«. Schlichting is a professor of physics didactics and worked at the University of Münster until his retirement.

To imagine the process in detail, the image of a layer of water that hits the water surface under the influence of gravity helps. There is air between the two, which is pushed to the side.

That’s not a problem as long as it’s free to flow. However, as soon as the distance falls below a certain level, more and more typical interfacial forces determine the flow behavior of the escaping air. It is simultaneously displaced and compressed in the increasingly narrow gap. Because of this, the gas particles can no longer move freely and independently in space. Rather, the profile of a laminar flow is created. That is, the air molecules at the boundary with the water stick to it while their speed increases toward the center. In addition, the viscosity of the air increases with a smaller gap width. This manifests itself in an increased frictional force that slows down the air flow. To put it bluntly, this strengthens the conditions in the shell and stabilizes them against disruptive influences.

However, the boundaries of the air squeezed in this way are not immobile as in solid walls, but fluid. So the surrounding water could be carried along as a result of the friction force. The airflow would then not be slowed down, but would remain fast, thin and fragile. This would prevent an antibubble from developing.

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