SOUND : Water Levitated by Tibetan Singing Bowls By Stephen Ornes
The Dalai Lama might like this one. Tibetan singing bowls, ancient instruments used for meditation, can be manipulated to produce droplets that levitate, bounce and skip across water.
When one adds water to a Tibetan singing bowl and plays – often by tracing the edge with a mallet – the bowl's haunting sound is accompanied by ripples on the water's surface. That's because the mallet pushes on the side of the bowl – made from bronze alloy that is more malleable than glass – and deforms it on a microscopic scale.
The deformation pushes on the air and the water, forming waves. The air waves are sound; the water waves race around the ring. If they are sufficiently excited, the waves break and eject droplets. The same happens in a wine glass, though at higher resonant frequencies.
Bowled over Denis Terwagne, at the University of Liège in Belgium, says the study began when a "sound healer" in Florida pointed out the droplet phenomenon and sent a bowl to co-author John Bush, a mathematician at the Massachusetts Institute of Technology. "We were motivated by curiosity," Terwagne says.
Terwagne and Bush didn't excite the bowls with a mallet, which produces rich sounds comprising different frequencies. Instead, they used a speaker to excite the bowl at particular frequencies. With a high-speed camera, the researchers recorded the droplets' ejection and behaviours. With the slowed-down footage, they measured the locations and movements. The video shows droplets levitating on the surface and the rim. The higher frequency of the song, the smaller the resulting drops.
The bowls suggest new ways to create and manipulate droplets that skitter across an air film atop a surface. Octávio Inácio, who researches the acoustics of singing bowls at the Polytechnic Institute of Porto, Portugal, says it might be possible to separate liquids or mix materials using vibrations of the container.