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Why leaky taps make that ‘plink’ noise — and what we can do about it

Whether it’s curing epidemics, figuring out how to knock Earth-bound asteroids off course, or working out the rocket science that will let us colonize Mars, there are some problems we’re glad to know the world’s best and brightest are focused on solving. A possible fourth? Giving us insight into out why in the name of all that is good do leaky taps drip so darn loudly — and what we can do about it.

This last conundrum was the focus of a recent research project from investigators at the U.K.’s University of Cambridge. While water droplets have been a source of scientific interest for more than a century, this is the first time anyone has tried to figure out the physical explanation behind the highly distinctive sound.

“This study was all about finding out what was behind the well known ‘plink’ sound produced by a drop of water falling into some more water — for example, from a leaking roof into a bucket, or a tap into a sink,” researcher Sam Phillips, who carried out the work for his masters’ degree dissertation, told Digital Trends.

The team used ultra high-speed cameras and sensitive microphones, placed above and below the water surface. With this setup, they then took slow-motion videos of water droplets impacting the water surface and synchronized these images with the sound recording. Their research demonstrated that the sound is, in fact, driven not by the splash that we see, but by a tiny vibrating air bubble which gets trapped under the surface of the water.

“We also found that the way this bubble produces the sound is that its vibrations cause the water surface itself to oscillate, with the surface then acting like a piston to drive sound waves into the air,” Phillips continued.

So how do we stop these sounds, so that we will never again have another night’s sleep disrupted by an unreasonably loud leaky tap?

“As part of confirming that the trapped air bubble really was causing all the sound we tried to prevent it from being produced,” Phillips said. “One way we did this was by adding a small amount of washing up liquid, or detergent, to the water surface to change the surface tension and prevent the bubble from being trapped under the water. In our experiment this worked, so it may be that adding a small amount of washing up liquid to the water that is being dripped into is a simple solution to stop the sound.”

A paper describing the work was recently published in the journal Scientific Reports.

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