The Unusual Physics of an Upside-Down Boat Flips Previous Understandings of the Law of Buoyancy

Since the time of ancient Greek mathematician Archimedes, the science of how boats can float on water has remained the same. He explained that the displaced water's upward force balances the downward force by gravity.

Almost 70 years ago, Russian Nobel prizewinning physicist Pyotr Kapitsa described the process of levitating liquid in mid-air. He said that rapidly shaking a pendulum up and down balances it upright rather than falling back to its original position. Scientists have used this concept to make liquids levitate mid-air to get air bubbles to sink.

The new study used this concept and suggested that the law of buoyancy could also be flipped. The physicists have managed to float tiny toy boats on the underside layer of the levitating liquid. Their study opens up new possibilities for nautical concepts that flip the idea of buoyancy.

The Serendipitous Discovery of the Flipped Buoyancy

Engineer Vladislav Sorokin of the University of Auckland said that the study is very counterintuitive and unexpected. Physicist Emmanuel Fort at ESPCI Paris, whose laboratory focuses on optics and imaging, said that there was serendipity in this discovery.

Previous studies suggest that every time a part of the levitating fluid tries to drip, a force from the shaking pushes it back to prevent from breaking and traps air underneath it.

However, Fort was unaware of this prior study. He and his colleagues got their inspiration in doing their research from Kapitsa's pendulum in which they tried replicating it by building a plexiglass container on top of a vibrating machine.

The container was filled with silicon oil or glycerol, and they used a needle to inject a layer of air at the bottom of the container. They found that the liquid levitated mid-air.

But after realizing that the phenomenon was already discovered decades ago, Fort and his team tweaked their experiment further. They placed tiny beads to the levitating liquid and saw that the beads were floating stable on the liquid layer's underside.

Fort said that it was completely unexpected. To push it further to the next level, they replaced the small beads by some small toy boats and discovered that they could make two boats float at the same time but the opposite side: one at the top and the other at the levitating liquid's underside.

Buoyancy in the Underside of the Levitating Liquid

To explain the buoyancy mirrored in the underside of the levitating liquid, the researchers created a model. According to them, strong vibrations have prevented the liquid from falling down or up to the liquid as it would have usually done if small disturbances are applied to it.

The vibration kept the object stable on the underside, where the gravity that pulls it down and buoyancy that pulls it up are balanced.

But it is not yet clear if this phenomenon serves any purpose as vibrations have been used to eliminate air bubbles for chemical reactions and mineral processing. It would take more research to determine how this phenomenon can be of use other than discovering that there is more to understand about vibrations.

The team used liquid that not more than half a liter, but researchers said that it might be increased provided that the strength of shaking is also increased. They also noted that their experiment does not apply to water but only to viscous liquids.

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