Skip to content
Support Us

We need your help now

Support from readers like you keeps The Journal open.

You are visiting us because we have something you value. Independent, unbiased news that tells the truth. Advertising revenue goes some way to support our mission, but this year it has not been enough.

If you've seen value in our reporting, please contribute what you can, so we can continue to produce accurate and meaningful journalism. For everyone who needs it.

Andrey_Popov via Shutterstock

Cambridge scientists went to the bother of finding out more about the sound of a dripping tap

They have also identified a simple solution to stop it.

SCIENTISTS HAVE SOLVED the riddle behind one of the most recognisable, and annoying, household sounds – the dripping tap.

And crucially, they have also identified a simple solution to stop it, which most of us already have in our kitchens.

In an unusual study, researchers from the University of Cambridge used ultra-high-speed cameras and modern audio capture techniques and found that the “plink, plink” sound produced by a water droplet hitting a liquid surface is caused not by the droplet itself, but by a small bubble of air trapped beneath the water’s surface.

In addition, the researchers found that changing the surface tension or the surface, for example by adding dish soap, can stop the sound.

Mystery through the years 

Despite the fact that humans have been kept awake by the sound dripping water from a leaky tap or roof for generations, the exact source of the sound has not been known until now.

“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, who led the research.

“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 first decided to investigate this problem while a friend who had a small leak in the roof of his house. Agarwal leads the Acoustics Lab, and his research investigates acoustics and aerodynamics of aerospace, domestic appliances and biomedical applications.

“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. The next day I discussed it with my friend and other visiting academic, and we were all surprised that no one had actually answered the question of what causes the sound,” he said.

Water droplets have been a source of scientific mystery for more than a century.

However, the fluid mechanics of a water droplet hitting a liquid surface are well-know – when the droplet hits the surface, it causes the formation of a cavity, which quickly recoils due to the surface tension of the liquid, resulting in a rising column of liquid.

Since the cavity recoils so fast after the droplet’s impact, it causes a small air bubble to get trapped underwater.

The answer

Previous studies have suggested that the “plink” sound is caused by the impact itself, the resonance of the cavity, or the underwater sound field pushing through the water surface, but have not been able to confirm this experimentally.

In their experiment, the Cambridge researchers found that somewhat counter-intuitively, the initial splash, the formation of the cavity, and the jet of the liquid are all effectively silent.

The source of the 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,” Phillips said.

For the “plink” sound to be significant, the trapped air bubble needs to be close to the bottom of the cavity caused by the drop impact.

The bubble then drives vibrations of the water surface at the bottom of the cavity, acting like a piston driving sound waves into the air.

According to the researchers, while the study was purely curiosity-driven, the results could be used to develop more efficient ways to measure rainfall or to develop a convincing synthesised sound for water droplets in gaming or movies, which has not yet been achieved.

The study has been published in the Scientific Reports journal.

Readers like you are keeping these stories free for everyone...
A mix of advertising and supporting contributions helps keep paywalls away from valuable information like this article. Over 5,000 readers like you have already stepped up and support us with a monthly payment or a once-off donation.

Close
11 Comments
This is YOUR comments community. Stay civil, stay constructive, stay on topic. Please familiarise yourself with our comments policy here before taking part.
Leave a Comment
    Install the app to use these features.
    Mute LoyalIrish Citizen
    Favourite LoyalIrish Citizen
    Report
    Dec 26th 2011, 10:28 AM

    I agree with almost everything that you have written.

    My reasons for these things to happen, which allows them to get away with
    with what everybody knows to be wrong is the use of opinions in law.

    The purpose of using opinions in law is to commit crime, hide the details
    of the crimes, circumvent the rules and avoid prosecution.

    Irish Courts have been allowing the use of opinions over 8300 times since
    1922, which is in complete contradiction to people questioning evidence.

    The only way get the use of opinions in law to commit crimes is to falsify
    the rule books of Ireland.

    If you study opinions in law it will explain everything that you need to
    know, which you can get access to the laws of Ireland at the Attorney
    Generals website :- http://www.irishstatutebook.ie/home.html

    Regards

    LoyalIrishCitizen

    26
    Install the app to use these features.
    Mute Pat Ambrose
    Favourite Pat Ambrose
    Report
    Dec 26th 2011, 1:36 PM

    I have seen people getting jail for stealing groceries, yet the bankers, politicians, (some) get away scot free to rob and plunder all over again.

    23
    Install the app to use these features.
    Mute Dermot Purcell
    Favourite Dermot Purcell
    Report
    Dec 26th 2011, 10:40 AM

    Your article nick on white collar crime is spot on except for you call it wrongdoing i call it FRAUD ,can you imagine if there was a real investigation in to the banks and seanie was in there spilling the beans on cowen and bertie judges and all the heads and top level managment of every institution in this country ,can people imagine the fall out and our image abroad would be in tatters, this is why nobody going to jail in this country .

    23
    Install the app to use these features.
    Mute Ultan Quirke
    Favourite Ultan Quirke
    Report
    Dec 26th 2011, 11:19 AM

    Our image abroad is already in tatters.

    30
    Install the app to use these features.
    Mute Richard Coady
    Favourite Richard Coady
    Report
    Dec 26th 2011, 11:24 AM

    Great article Nick. Engrossing as always. Would love to read something from you on the actual workings of bankruptcy and it’s day to day effects, what you can and can’t do. You allude to your direct experience with money lenders. Any chance of writing a book on your experience of post barings?

    18
    Install the app to use these features.
    Mute Chris Coffey
    Favourite Chris Coffey
    Report
    Dec 26th 2011, 2:03 PM

    Brilliant stuff, as always. I’m starting to click into Nicks articles the minute I see his name. No better reading on here then the articles by people who know exactly what their talking about, not to mention his extra insight into the risks that people in finance can take.

    15
    Install the app to use these features.
    Mute Joe Sixtwo
    Favourite Joe Sixtwo
    Report
    Dec 26th 2011, 12:13 PM

    Nice piece of work Nick.

    13
    Install the app to use these features.
    Mute Jean Morel
    Favourite Jean Morel
    Report
    Dec 26th 2011, 9:46 PM

    I said Ireland was a land of criminals way back in the mid 80′s.

    5
    Install the app to use these features.
    Mute Ardo Ci
    Favourite Ardo Ci
    Report
    Dec 27th 2011, 10:28 AM

    Well said, Nick! Well said, indeed. Ireland is no longer the ‘ land of saints and scholars ‘ but rather the ‘ land of crooks and criminals’. The ordinary people don’t deserve what’ s happening. What we need now is an ‘Irish’ Cromwell to rise from among us.

    5
    Install the app to use these features.
    Mute Sheila Murphy
    Favourite Sheila Murphy
    Report
    Dec 28th 2011, 1:10 PM

    I must say I couldn’t agree more with the points he’s making about the tribunals; complete waste of millions & millions of Euros….. again no actions taken from any of them. Ridiculous set-ups.

    And I’ve seen the ads on UK TV to which he refers re the pay-day quick loans. Think about in whose hands those loans end up in, when you can’t afford to repay their exorbitant interest amounts??? You don’t think that they eventually don’t get sold on to very unscrupulous people who don’t care HOW they get their money back??? Very dangerous. And again it’s the most financially vulnerable that end up in these situations…….. very sad,

    2
    Install the app to use these features.
    Mute Geoffrey Collins
    Favourite Geoffrey Collins
    Report
    Dec 28th 2011, 10:16 AM

    Why is nick treated with such fawning when he was guilty of the same financial gambling as happened in Anglo? I enjoy his articles also but is there not a hint of kettle pot black?

    2
    Install the app to use these features.
    Mute Sheila Murphy
    Favourite Sheila Murphy
    Report
    Dec 28th 2011, 1:08 PM

    well he went to prison for it Geoffrey and served his time. More than has happened to the bankers here unfortunately. Depressing thought.

    It’s interesting to read an opinion of one who was there, so to speak.

    4
    Install the app to use these features.
    Mute Felim O'Neill
    Favourite Felim O'Neill
    Report
    Jan 6th 2012, 12:42 AM

    Question to Nick.

    It always interests me that the Financial Services professional view tends to be subjective and overly fascinated with itself.

    As a challenge, if you had a vision of “Next Gen” Capitalism, what would it look like? Hopefully as a thinking man, with all your training and experience, you might secretly have a vision for how stuff should work next time around. If so, please share it with us!

    While many agree we need to put checks/balances in place before next Bull Run, we need to put todays Bear on some sort of financial Prozac for the nerves.

    Hope and Vision please.

    Thanks again,

    Felim O’Neill

    1
Submit a report
Please help us understand how this comment violates our community guidelines.
Thank you for the feedback
Your feedback has been sent to our team for review.

Leave a comment

 
cancel reply
JournalTv
News in 60 seconds