Bubbles can be made to “gallop” across the roof of a liquid-filled container simply by shaking it up and down – a surprise discovery that could be exploited as a cleaning technique.
at the University of North Carolina at Chapel Hill and his colleagues were studying the behaviour of waves in a sealed container using vibrations when they made a chance discovery. The team found that shaking the liquid-filled chamber up and down at particular frequencies caused a bubble that had mistakenly entered the container to begin moving horizontally.
Investigating further, the researchers found that this movement was caused by the bubbles changing shape. Left to their own devices, bubbles are normally spherical, but the team discovered that vibrating the chamber at the right frequency caused the bubbles to break their symmetry and become lopsided. Once this happened, the bubbles would start to “gallop” by cycling through a series of wiggling shapes, with one side fatter than the other in an alternating pattern. This wiggling pushed the bubbles against the surrounding liquid, moving them forwards.
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“I think it’s remarkable that we found such a beautiful effect in a field that has been studied so much,” says Sáenz.
The researchers also found that the bubbles could gallop in three distinct ways, depending on the frequency of the vibrations: forward in a straight line, spinning in place, or moving in multiple directions through chaotic jolts. By exploiting these behaviours, the researchers found that they could move the bubbles through a complex fluid maze or sort them into different-sized groups.
at Cornell University in New York state says that the ability to precisely control the galloping motion could have many different practical applications in the future. For example, Sáenz and his team showed that the chaotic galloping motion could be used to remove dust particles from surfaces by dislodging the particles and sweeping them beneath the bubble. In this way, galloping bubbles can act like tiny robotic vacuum cleaners, says Sáenz. This could make cleaning more sustainable by reducing the amount of chemicals needed, says Jung.
Nature Communications
