How to Stop the Sound of a Dripping Faucet Instantly, According to Science

It’s tempting to think that the “plink” sound produced by a falling water droplet on a liquid surface is caused by the droplet itself, but new research points to an unexpected source of this familiar, yet annoying, sound. Excitingly, the researchers have also identified a neat hack to stop it.

The sound produced when a water droplet hits a liquid surface is caused by the vibrating movements of a small air bubble trapped beneath the water’s surface, according to new researchpublished today in Science Reports.

Seems weird we are only learning this now, but it’s a mystery that’s vexed scientists for over a hundred years. Back in 1908, American scientist Arthur Worthington conducted his “Study of Splashes,” which produced the earliest known photos of droplet impacts. His work generated considerable interest, and by the 1920s scientists were investigating the curious sounds produced by water droplets. Many theories were proposed over the years to explain the distinctive “plink” noise, but no experimental studies were able to confirm the various hypotheses.

“A lot of work has been done on the physical mechanics of a dripping tap, but not very much has been done on the sound,” Anurag Agarwal, a researcher at the Department of Engineering at Cambridge University and the lead author of the new study, said in a statement. “But thanks to modern video and audio technology, we can finally find out exactly where the sound is coming from, which may help us to stop it.”

Seems weird we are only learning this now, but it’s a mystery that’s vexed scientists for over a hundred years. Back in 1908, American scientist Arthur Worthington conducted his “Study of Splashes,” which produced the earliest known photos of droplet impacts. His work generated considerable interest, and by the 1920s scientists were investigating the curious sounds produced by water droplets. Many theories were proposed over the years to explain the distinctive “plink” noise, but no experimental studies were able to confirm the various hypotheses.

“A lot of work has been done on the physical mechanics of a dripping tap, but not very much has been done on the sound,” Anurag Agarwal, a researcher at the Department of Engineering at Cambridge University and the lead author of the new study, said in a statement. “But thanks to modern video and audio technology, we can finally find out exactly where the sound is coming from, which may help us to stop it.”

However, the new observations made by Agarwal’s team showed that none of these things, the initial splash, the formation of the cavity, or the jet of liquid, produced any sounds of consequence. Instead, the source of the “plink” comes from the trapped air bubble itself.

“Using high-speed cameras and high-sensitivity microphones, we were able to directly observe the oscillation [i.e. vibrations] of the air bubble for the first time, showing that the air bubble is the key driver for both the underwater sound, and the distinctive airborne ‘plink’ sound,” said Sam Phillips, a co-author of the new study. “However, the airborne sound is not simply the underwater sound field spreading to the surface, as had been previously thought.”

Indeed, in order to produce a sound that’s loud enough to drive us batty up at night, the trapped air bubble needs to be close to the bottom of the cavity. The bubble then vibrates against the surface like a piston, driving sounds waves into the air. And into your ear.

The researchers also found that changes to the surface tension of the liquid surface can stop, or diminish, the sound. So for those of you with a leaky faucet, your best bet is to add a bit of dish soap to whatever container is catching the water drips. Simple. Who needs an expensive plumber when you’ve got fluid dynamics at your disposal?

Source: Gizmodo

 

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