Scientists Find Out How To Stop The Awful Sound Of A Dripping Tap

Posted: Jun 24 2018, 12:24am CDT | by , in News | Latest Science News

 
Scientists Find Out How to Stop the Awful Sound of a Dripping Tap
Credit: Sarah Collins (Cambridge University)

Researchers have found what causes the sound of a leaky tap and how we can fix it.

The sound of a leaky faucet is extremely annoying and may keep you awake all night. However, researchers believe they have identified the cause of this sound and also a simple solution to stop it.

Using ultra-high-speed cameras and advanced audio capture techniques, researchers from the University of Cambridge have found that the painfully familiar 'plink, plink' sound is not caused by the water droplet hitting a liquid surface. Instead, the noise is created by the movement of a small bubble of air trapped beneath the water’s surface. If we can change the surface tension of the water by adding something like a dish soap, we can prevent this sound.

“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," said lead researcher Dr. Anurag Agarwal from the University of Cambridge. "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."

Agarwal decided to investigate this problem while visiting a friend in Brazil in 2016. His friend’s house had a small leak in the roof. During the trip, Agarwal could not sleep at all because of the steady drip of a leaky roof.

"While I was being kept awake by the sound of water falling into a bucket placed underneath the leak, I started thinking about this problem," he said. "The next day I discussed it with my friend and another visiting academic, and we were all surprised that no one had actually answered the question of what causes the sound."

To find out, Agarwal set up an experiment. He placed an ultra-high-speed camera, a microphone, and an underwater microphone and used them to capture the exact moment a droplet falls into a tank of water.

Researchers have long known that a water droplet that hits the surface causes the formation of a cavity. The cavity quickly recoils due to the surface tension of the liquid and creates a small column of liquid. The speedy process also causes an air bubble to get trapped underwater.

Previous studies have suggested that the 'plink' sound is caused by the impact itself. In the latest effort, researchers have found that plink only occurs when a water droplet lands in the water. If it lands on a dry surface, it produces only a dull, heavy sound. This means that the actual source of sound is the trapped air bubble.

"Using high-speed cameras and high-sensitivity microphones, we were able to directly observe the oscillation 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 researcher Sam Phillips. "However, the airborne sound is not simply the underwater sound field spreading to the surface, as had been previously thought."

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