July 19, 2013
World's Slowest-Moving Drop Caught on Camera At Last
The once-forgotten "tar pitch" experiment has yielded results after a seven-decade wait
By Richard Johnston & Nature magazine
How long would you be willing to wait for a drop of the black stuff in Dublin? After 69 years, one of the longest-running laboratory investigations in the world has finally captured the fall of a drop of tar pitch on camera for the first time. A similar, better-known and older experiment in Australia missed filming its latest drop in 2000 because the camera was offline at the time.
The Dublin pitch-drop experiment was set up in 1944 at Trinity College Dublin to demonstrate the high viscosity or low fluidity of pitch — also known as bitumen or asphalt — a material that appears to be solid at room temperature, but is in fact flowing, albeit extremely slowly.
It is a younger and less well-known sibling of an experiment that has been running since 1927 at the University of Queensland in Brisbane, which Guinness World Records lists as the world’s longest-running laboratory experiment (see: Long-term research: Slow science ). Physicist Thomas Parnell set it up because he wanted to illustrate that everyday materials can exhibit surprising properties. In the past 86 years that experiment has yielded eight drops, with the ninth drop now almost fully formed and about to fall.
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Long wait John Mainstone has been custodian of the Queensland experiment since 1961, and has yet to see or capture the fall of a drop — unsurprising given that it takes 7 to 13 years for a drop to form, but only a tenth of a second for it to fall.
Pitch-drop experiments involve heating a sample of pitch and pouring it into a sealed glass funnel. The pitch is given time — three years in Parnell’s experiment — to settle and consolidate before the sealed stem of the funnel is cut.
The origins of the Dublin experiment are now lost to history. It may have been part of a push by the physicist and Nobel prizewinner Ernest Walton, a professor at Trinity College Dublin, to promote science demonstrations for educational purposes. Over the years, the identity of the scientist who began the experiment was forgotten, and the experiment lay unattended on a shelf where it continued to shed drops uninterrupted while gathering layers of dust.
Watching it fall Physicists at Trinity College recently began to monitor the experiment again. Last April they set up a webcam so that anyone could watch and try to be the first person ever to witness the drop fall live.
At around 5 o'clock in the afternoon on 11 July, physicist Shane Bergin and colleagues captured footage of one of the most eagerly anticipated and exhilarating drips in science. “We were all so excited,” Bergin says. “It’s been such a great talking point, with colleagues eager to investigate the mechanics of the break, and the viscosity of the pitch”.
The Trinity College team has estimated the viscosity of the pitch by monitoring the evolution of this one drop, and puts it in the region of 2 million times more viscous than honey, or 20 billion times the viscosity of water. The speed of formation of the drop can depend on the exact composition of the pitch, and environmental conditions such as temperature and vibration.
Asked about the value of this demonstration, Bergin’s colleague Denis Weaire says, “Curiosity is at the heart of good science, and the pitch drop fuels that curiosity”.
Scientists used to believe glass to be a slow-moving liquid as well — in part because old church window panes are thicker at the bottom — but it is now considered a solid .
And the next one Mainstone, who has spent most of his life waiting to see a drop fall with his own eyes, congratulated the Trinity College team. “I have been examining the video over and over again,” he says, ”and there were a number of things about it that were really quite tantalizing for a very long time pitch-drop observer like myself.”
The University of Queensland pitch-drop experiment can be viewed live via a webcam and has a broad following across the globe. The next Queensland drop is predicted to fall some time in 2013.
This article is reproduced with permission from the magazine Nature . The article was first published on July 18, 2013.
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Longest experiment sees pitch drop after 84-year wait
By Lisa Grossman and Celeste Biever
17 April 2014
Video: Pitch drops again in world’s longest experiment
The pitch has dropped – again. This time, the glimpse of a falling blob of tar, also called pitch, represents the first result for the world’s longest-running experiment.
Sadly however, the glimpse comes too late for a former custodian, who watched over the experiment for more than half a century and died a year ago.
Up-and-running since 1930, the experiment is based at the University of Queensland in Australia and seeks to capture blobs of pitch as they drip down, agonisingly slowly, from their parent bulk.
It was pipped to the post last year when a similar experiment, set up in 1944 at Trinity College Dublin in Ireland, captured the first ever video footage of a blob of pitch dropping .
In that instance, the blob separated from its parent bulk. By contrast, the Australian team filmed the collision between the ninth blob ever to fall and the eighth blob, which was sitting at the bottom of their beaker – but the ninth blob is still attached to the pitch above it.
Still, the Australian result is important because the experiment has a better set-up, says Stefan Hutzler , a member of the Trinity College Dublin team who used those results to calculate the pitch’s viscosity. “Theirs is in a glass container; they measure the temperature, measure the humidity as well,” he says. “Ours, we don’t really call it an experiment. It was really just sitting there on a shelf, going back to the 1940s.”
The fact that both experiments dropped within a year of each other is “just pure luck”, says Hutzler. Hot summer weather in Ireland last year may have influenced the timing.
The Queensland experiment already features in the Guinness World Records and won an IgNobel prize in 2005 . It was set up by physicist Thomas Parnell to illustrate that although pitch appears solid, shattering when hit with a hammer at room temperature, it is actually a very viscous liquid.
The eventual result follows several near misses, according to the University of Queensland. John Mainstone, who oversaw the experiment for more than 50 years until his death last August , missed observing the drops fall three times – by a day in 1977, by just five minutes in 1988 and, perhaps most annoying, in 2000, when the webcam that was recording it was hit by a 20-minute power outage.
“It’s a pity of course that the person in charge died about a year ago, so he never saw the drop,” Hutzler says. “He would have enjoyed that.”
The eighth and ninth drops each took about 13 years to fall, says current custodian Andrew White. By contrast, the seven drops that fell between 1930 and 1988 did so faster – at an average rate of one drop every eight years.
The next step is to see how long it takes the ninth drop to separate from the pitch above it: “It may tip over quickly or it might slow right down and take years to break away,” says White.
You can keep an eye on the ninth drop’s movements via a live web stream . The University of Queensland says it will work out who was watching when the pitch dropped and record their names for posterity.
The drop experiments show that the physics of a drop forming in a viscous material is still not well understood, Hutzler says – although he doesn’t think watching pitch for decades is necessarily the best way to study it. Using honey or some other less viscous fluid would give you better statistics.
“I think these experiments capture the imagination just because they go on for such a long time,” he says. The video of the drop in Dublin quickly went viral on YouTube. “Ironically, you have a very slow event happening, but the news spreads very quickly.”
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