Johannesburg - The plink-plink of a dripping tap has stolen the sleep of generations, forced unscheduled toilet calls and made emergency plumbers rich.
It might just be the most annoying recognisable household sound in the history of humankind, but fear not, for science has solved the riddle of the dripping tap - and how to stop it.
In research just released, scientists from the University of Cambridge have discovered that the plink-plink sound is produced not from the droplet itself but by the oscillation of a small bubble of air trapped beneath the water’s surface. This bubble then forces the water surface to vibrate and voilà! The plink sound is produced.
The scientists found this out through using high-speed cameras and modern audio capture techniques.
Until now the exact source of the dipping sound was not known.
“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 Dr Anurag Agarwal of Cambridge’s Department of Engineering. “But thanks to video and audio technology, we can finally find out exactly where the sound comes from, which may help us to stop it.”
Agarwal had decided to tackle the age-old riddle while visiting a friend who had a leak in the roof of his house.
“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.”
Agarwal set up an experiment that included an ultra-high-speed camera, a microphone and a hydrophone that recorded droplets falling into a tank of water.
“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 fellow researcher Sam Phillips. “However, the airborne sound is not simply the underwater sound field spreading to the surface, as had been previously thought.”
As for stopping the plink-plink sound, it’s easy, say the scientists.
Add dishwashing liquid to the water to change the surface tension, that should kill the sound.