Student Solves Physics Mystery That Stumped Scientists for a Century

A Bachelor's student at EPFL discovered why air bubbles don't appear to rise in narrow tubes, solving a 100-year-old conundrum.

For about 100 years, scientists haven't been able to figure out why air bubbles in a narrow vertical tube wouldn't rise up, seeming to stick to the insides instead. 

After all air bubbles contained in a cup of water rise to the surface and are easily explained by laws of science. The same, however, can't be said of air bubbles in narrow tubes. That is until now. 

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Air bubbles are moving, just really slowly 

A student at Switzerland's The Ecole Polytechnique fédérale de Lausanne (EPFL) research institute and university, solved the mystery that's perplexed scientists for all those years.

Wassim Dhaouad, a  Bachelor's student at the Engineering Mechanics of Soft Interfaces laboratory (EMSI) within EPFL's School of Engineering found the air bubbles aren't stuck they are just moving extremely slowly. Dhaouad discovered a film of liquid that is super thin forms around the bubble and as a result, it can rise freely. Dhaouad's research was published in the journal Physical Review Fluids

The college student joined the EMSI as a summer research assistant and participated in the research due to his interest, not expecting it to result in a published paper that solved a mystery that has stumped scientists for a century. 

 "I was happy to carry a research project early in my curriculum. It is a new way of thinking and learning and was quite different from a Homework set where you know there is a solution, although it may be hard to find. At first, We did not know if there would even be a solution to this problem," said Dhaouadi in a press release highlighting the research. 

Researchers relied on an optical interference method 

To determine what was going on with air bubbles in narrow tubes, the Bachelor's student enlisted John Kolinski, EMSI lab head. They used an optical interference method the measure the film, which included putting light on the air bubble in the tube and looking at the intensity of the light reflected off the tube.

Using the light that was reflected from the inner wall of the tube and the bubble's surface they determined the film was just a few dozen nanometers in thickness. Through their work, they also found that when the heat was applied to the film it would change its shape. Once the heat was removed the bubble would return to its prior shape. 

The measurements also prove the bubbles are moving, but at a pace that is too slow for humans to see. "Because the film between the bubble and the tube is so thin, it creates a strong resistance to flow, drastically slowing the bubbles' rise," Kolinski said in a press release announcing the research.

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