View source for Pitch drop experiment

{{Short description|Long-term experiment measuring the flow of pitch}}
{{Distinguish|oil drop experiment}}
{{Use Australian English|date=June 2020}}
{{Use dmy dates|date=September 2020}}
[[Image:University of Queensland Pitch drop experiment-white bg.jpg|thumb|right|upright|The [[University of Queensland]] pitch drop experiment, demonstrating the [[viscosity]] of [[bitumen]].]]
A '''pitch drop experiment''' is a [[long-term experiment]] which measures the flow of a piece of [[Pitch (resin)|pitch]] over many years. "Pitch" is the name for any of a number of highly [[Viscosity|viscous]] liquids which appear solid, most commonly [[bitumen]], also known as asphalt. At room temperature, tar pitch flows at a very low rate, taking several years to form a single drop.

==University of Queensland experiment==
[[Image:Pitch drop experiment with John Mainstone.jpg|thumb|left|The [[University of Queensland]] pitch drop experiment, featuring its custodian, John Mainstone (taken in 1990, two years after the seventh drop and 10&nbsp;years before the eighth drop fell).]]
The best-known version<ref name=" BBC1" /> of the [[experiment]] was started in 1927 by [[Thomas Parnell (scientist)|Thomas Parnell]] of the [[University of Queensland]] in [[Brisbane]], Australia, to demonstrate to students that some substances which appear solid are highly viscous fluids.<ref name="NS_Queensland">{{cite journal |title=Feedback |journal=New Scientist |date=15 November 1984 |page=38|issn=0028-6664 |url=https://books.google.com/books?id=siZ1j_5wdqwC&pg=PA38 |access-date=5 May 2023 }}</ref> Parnell poured a heated sample of the pitch into a sealed [[funnel]] and allowed it to settle for three years.<ref name="EurJPhys_Queensland">{{cite journal |first1=R |last1=Edgeworth |first2=B J |last2=Dalton |first3=T |last3=Parnell |title=The pitch drop experiment |year=1984 |journal=European Journal of Physics |volume=5 |issue=4 |pages=198–200 |doi=10.1088/0143-0807/5/4/003 |bibcode=1984EJPh....5..198E |s2cid=250769509 |url=https://iopscience.iop.org/article/10.1088/0143-0807/5/4/003 |url-access=subscription }}</ref> In 1930, the seal at the neck of the funnel was cut, allowing the pitch to start flowing. A glass dome covers the funnel and it is placed on display outside a lecture theatre.<ref name="life">{{Cite news|author=Dalton|first=Trent|date=6 April 2013|title=Pitch fever|newspaper=The Australian|url=http://www.theaustralian.com.au/news/features/pitch-fever/story-e6frg8h6-1226613215795|url-status=dead|access-date=9 July 2013|archive-url=https://web.archive.org/web/20130406075404/http://www.theaustralian.com.au/news/features/pitch-fever/story-e6frg8h6-1226613215795|archive-date=6 April 2013}}</ref> Each droplet forms and falls over a period of about a [[decade]].

Between 1961 and 2013, the experiment was supervised by John Mainstone {{small|{{bracket|[[:de:John Mainstone|de]]}}}}.

The seventh drop fell at approximately 4:45&nbsp;p.m. on 3 July 1988, while the experiment was on display at Brisbane's [[World Expo 88]]. However, apparently no one witnessed the drop fall itself;<ref>[https://www.newspapers.com/clip/113380954/ Just a drip – but what great timing], ''[[Sydney Morning Herald]]'', 16 July 1988, page 3.</ref> Mainstone had stepped out to get a drink at the moment it occurred.<ref name=" BBC1" />

The eighth drop fell on 28 November 2000, allowing experimenters to calculate the pitch as having a [[viscosity]] of approximately 230&nbsp;[[1,000,000,000|billion]] times that of [[water]].<ref name="pitchdrop">{{cite web|last1=Edgeworth|first1=R.|last2=Dalton|first2=B.J.|last3=Parnell|first3=T.|title=The Pitch Drop Experiment|url=http://www.physics.uq.edu.au/physics_museum/pitchdrop.shtml|url-status=dead|archive-url=https://web.archive.org/web/20130328064508/http://www.physics.uq.edu.au/physics_museum/pitchdrop.shtml|archive-date=28 March 2013|access-date=15 October 2007|publisher=The University of Queensland Australia}}</ref>

This experiment is recorded in [[Guinness World Records]] as the "world's longest continuously running laboratory experiment",<ref name="smp.uq.edu.au">{{cite web|title=The Pitch Drop Experiment|url=http://smp.uq.edu.au/content/pitch-drop-experiment|url-status=live|archive-url=https://web.archive.org/web/20200615174548/https://smp.uq.edu.au/pitch-drop-experiment|archive-date=15 June 2020|access-date=17 August 2016|website=The University of Queensland Australia: School of Mathematics and Physics|date=6 January 2016}}</ref> and it is expected there is enough pitch in the funnel to allow it to continue for at least another hundred years. This experiment is predated by two other (still-active) scientific devices, the [[Oxford Electric Bell]] (1840) and the [[Beverly Clock]] (1864), but each of these has experienced brief interruptions since 1937.

The experiment was not originally carried out under any special controlled atmospheric conditions, meaning the viscosity could vary throughout the year with fluctuations in [[temperature]].  Sometime after the seventh drop fell (1988), air conditioning was added to the location where the experiment takes place. The lower average temperature has lengthened each drop's stretch before it separates from the rest of the pitch in the funnel, and correspondingly the typical interval between drops has increased from eight years to 12–13 years.

In October 2005, Mainstone and Parnell were awarded the [[Ig Nobel Prize]] in physics, a parody of the [[Nobel Prize]], for the pitch drop experiment.<ref name="VPsJL">[http://improbable.com/ig/winners/#ig2005 The 2005 Ig Nobel prize winners]. Improbable Research. Retrieved 6 July 2013.</ref> Mainstone subsequently commented:

{{blockquote|I am sure that Thomas Parnell would have been flattered to know that Mark Henderson considers him worthy to become a recipient of an Ig&nbsp;Nobel prize. Professor Parnell's award citation would of course have to applaud the new record he had thereby established for the longest lead-time between the performance of a seminal scientific experiment and the conferral of such an award, be it a Nobel or an Ig&nbsp;Nobel prize.<ref name="Mainstone-Ig">{{cite web |url=http://smp.uq.edu.au/content/comment-professor-mainstone |title=A Comment from Professor Mainstone |last=Mainstone |first=John |publisher=[[University of Queensland]] |access-date=5 November 2012 |url-status=dead |archive-url=https://web.archive.org/web/20121115170011/http://smp.uq.edu.au/content/comment-professor-mainstone |archive-date=15 November 2012}}</ref>}}

The experiment is monitored by a [[webcam]]<ref name="thetenthwatch.com">{{Cite web|url=http://www.thetenthwatch.com/|title=The Tenth Watch for the ninth Pitch Drop}}</ref> but technical problems prevented the November 2000 drop from being recorded.<ref name="smp.uq.edu.au" /> The pitch drop experiment is on public display on Level&nbsp;2 of Parnell building in the [[School of Mathematics and Physics]] at the [[St Lucia, Queensland|St Lucia]] campus of the [[University of Queensland]]. Hundreds of thousands of Internet users check the live stream each year.<ref name="life" />

John Mainstone died on 13 August 2013, aged 78, following a [[stroke]].<ref name="xkAbQ">{{cite web|last=Helsel|first=Phil|date=27 August 2013|title=Professor in charge of famous 'Pitch Drop' experiment for 50 years dies waiting to see it in action|url=http://www.nypost.com/p/news/international/professor_never_charge_event_famous_AKmMGqJi1lfJ0J3xbxW8fJ|url-status=live|archive-url=https://web.archive.org/web/20200615174812/https://nypost.com/2013/08/27/professor-in-charge-of-famous-pitch-drop-experiment-for-50-years-dies-waiting-to-see-it-in-action/|archive-date=15 June 2020|access-date=27 August 2013|work=New York Post}}</ref> Custodianship then passed to Andrew White.<ref name="calligeros">{{Cite web|last=Calligeros|first=Marissa|date=27 August 2013|title=Pitch drop has new custodian after physicist's death|url=https://www.brisbanetimes.com.au/national/queensland/pitch-drop-has-new-custodian-after-physicists-death-20130827-2sne4.html|url-status=live|archive-url=https://web.archive.org/web/20200615174951/https://www.brisbanetimes.com.au/national/queensland/pitch-drop-has-new-custodian-after-physicists-death-20130827-2sne4.html|archive-date=15 June 2020|access-date=15 June 2020|website=Brisbane Times|language=en}}</ref>

The ninth drop touched the eighth drop on 12 April 2014;<ref name="www.uq.edu.au_news">{{cite web|date=17 April 2014|title=Pitch drop touches down – oh so gently|url=http://www.uq.edu.au/news/article/2014/04/pitch-drop-touches-down-%E2%80%93-oh-so-gently|url-status=live|archive-url=https://web.archive.org/web/20200615175106/http://www.uq.edu.au/news/article/2014/04/pitch-drop-touches-down-%E2%80%93-oh-so-gently|archive-date=15 June 2020|access-date=19 April 2014|publisher=The University of Queensland Australia}}</ref><ref name="usRFt">{{cite news|author=Cantor|first=Matt|date=18 April 2014|title=Big News in World's Longest Experiment, Drop of pitch falls after 13 years of waiting|work=Newser|publisher=[[Newser.com]]|url=http://www.newser.com/story/185539/big-news-in-worlds-longest-experiment.html|url-status=dead|access-date=18 April 2014|archive-url=https://web.archive.org/web/20140418191701/http://www.newser.com/story/185539/big-news-in-worlds-longest-experiment.html|archive-date=18 April 2014}}</ref><ref name="theconversation.com">{{cite web|date=10 November 2014|title=Explainer: the pitch drop experiment|url=https://theconversation.com/explainer-the-pitch-drop-experiment-33734|url-status=live|archive-url=https://web.archive.org/web/20141213123150/https://theconversation.com/explainer-the-pitch-drop-experiment-33734|archive-date=13 December 2014|publisher=[[The Conversation (website)|The Conversation]]}}</ref> however, it was still attached to the funnel. On 24 April, Professor White decided to replace the beaker holding the previous eight drops before the ninth drop fused to them (which would have permanently affected the ability of further drops to form). While the bell jar was being lifted, the wooden base wobbled and the ninth drop snapped away from the funnel.<ref name="ninthdrop">{{cite news|last1=White|first1=Andrew|last2=Baglot|first2=Julie|date=24 April 2014|title=Pitch Drop Experiment enters an exciting new era|publisher=The University of Queensland Australia|url=http://www.uq.edu.au/news/article/2014/04/pitch-drop-experiment-enters-exciting-new-era|url-status=live|access-date=25 April 2014|archive-url=https://web.archive.org/web/20200615175538/http://www.uq.edu.au/news/article/2014/04/pitch-drop-experiment-enters-exciting-new-era|archive-date=15 June 2020}}</ref>

===Timeline===
Timeline for the University of Queensland experiment:

{| class="wikitable"
! rowspan="2" | Date
! rowspan="2" | Event
!colspan="3"| Duration
|-
!Years
!Months
!Bar chart
|-
| align="right" |1927||Hot pitch poured|| colspan="3" |
|-
| align="right" |October 1930||Stem cut|| colspan="3" |
|-
| align="right" |December 1938||1st drop fell||8.1|| {{bartable|98}}
|-
| align="right" |February 1947||2nd drop fell||8.2||  {{bartable|99}}
|-
| align="right" |April 1954||3rd drop fell||7.2||  {{bartable|86}}
|-
| align="right" |May 1962||4th drop fell||8.1||  {{bartable|97}}
|-
| align="right" |August 1970||5th drop fell||8.3||  {{bartable|99}}
|-
| align="right" |April 1979||6th drop fell||8.7||  {{bartable|104}}
|-
| align="right" |July 1988||7th drop fell||9.2||  {{bartable|111}}
|-
| align="right" |November 2000||8th drop fell{{efn-ua|After the 7th drop, air conditioning was installed, lowering the average temperature.}} ||12.3||  {{bartable|148}}
|-
| align="right" |April 2014||9th drop fell{{efn-ua|12 April 2014: 9th drop touched 8th drop; 24 April 2014: 9th drop separated from funnel during beaker change.}}||13.4||  {{bartable|161}}
|}
{{notelist-ua}}

==Trinity College Dublin experiment==
The pitch drop experiment at [[Trinity College Dublin]] in Ireland was started in October 1944 by an unknown colleague of the Nobel Prize winner [[Ernest Walton]] while he was in the physics department of Trinity College. This experiment, like the one at University of Queensland, was set up to demonstrate the high viscosity of pitch. This physics experiment sat on a shelf in a lecture hall at Trinity College unmonitored for decades as it dripped a number of times from the funnel to the receiving jar below, also gathering layers of dust.<ref name="Johnson_Nature">{{cite journal | last = Johnston | first = Richard | title = World's slowest-moving drop caught on camera at last | journal = Nature | publisher = [[Nature Publishing Group]] | date = 18 July 2013 | doi = 10.1038/nature.2013.13418 | s2cid = 139012227 | url = http://www.nature.com/news/world-s-slowest-moving-drop-caught-on-camera-at-last-1.13418 | access-date = 15 March 2014| url-access = subscription }}</ref><ref name="JVs9y">{{cite web | title = Trinity College experiment succeeds after 69 years | publisher = [[RTÉ News]] | date = 19 July 2013 | url = http://www.rte.ie/news/2013/0717/463097-trinity-college-dublin-pitch-experiment/ | access-date = 19 July 2013}}</ref><ref name="nkLmc">{{cite web | last = Garber | first = Megan | title = The 3 Most Exciting Words in Science Right Now: 'The Pitch Dropped' | work = [[The Atlantic]] | date = 18 July 2013 | url = https://www.theatlantic.com/technology/archive/2013/07/the-3-most-exciting-words-in-science-right-now-the-pitch-dropped/277919/ | access-date = 19 July 2013}}</ref>

In April 2013, about a decade after the previous pitch drop, physicists at Trinity College noticed that another drip was forming. They moved the experiment to a table to monitor and record the falling drip with a webcam, allowing all present to watch.  The pitch dripped around 17:00&nbsp;[[Irish Standard Time|IST]] on 11 July 2013, marking the first time that a pitch drop was successfully recorded on camera.

Based on the results from this experiment, the Trinity College physicists estimated that the viscosity of the pitch is about two million times that of honey, or about 20&nbsp;billion times the viscosity of water.<ref name="Johnson_Nature" />

==University of St. Andrews experiment==
A pitch drop experiment was begun at the [[University of St Andrews]] in 1927, the same year as the Queensland experiment. No evidence has emerged of any contact between Parnell and the instigator or instigators of the St. Andrews experiment. The pitch in the St. Andrews experiment flows in a largely steady, but extremely slow, stream.<ref>{{cite web |url=https://www.uq.edu.au/news/article/1999/02/experiment-reaches-delicate-pitch |title=Experiment reaches delicate pitch |access-date=15 July 2022 }}</ref> At some stage (likely in 1984) St. Andrews professor [[John F. Allen (physicist)|John Allen]] modified the St. Andrews experiment to bring its setup closer to that of the University of Queensland experiment.<ref name="NS_St_Andrews">{{cite journal |title=Feedback |journal=New Scientist |date=13 December 1984 |page=32 |issn=0028-6664 |url=https://books.google.com/books?id=74PgZAHPw38C&pg=PA32 |access-date=5 May 2023 }}</ref>

==Aberystwyth University experiment==
In 2014, media reported that a pitch drop experiment had been recently rediscovered at [[Aberystwyth University]] in Wales. Dating from 1914, it predates the Queensland experiment by 13 years. But as the pitch is more viscous (or the average temperature lower) this experiment has not yet produced its first drop and is not expected to for over 1,000 years.<ref name="BBC1">{{cite web|last1=Webb|first1=Jonathan|date=26 July 2014|title=Tedium, tragedy and tar: The slowest drops in science|url=https://www.bbc.co.uk/news/science-environment-28402709|url-status=live|archive-url=https://web.archive.org/web/20200615173707/https://www.bbc.com/news/science-environment-28402709|archive-date=15 June 2020|access-date=26 July 2014|website=BBC News|publisher=BBC}}</ref><ref name="DigitalPC">{{cite web|last1=Shane D Bergin|last2=Stefan Hutzler|last3=Denis Weaire|title=The drop heard round the world|date=May 2014|url=http://physicsworld.com/cws/article/indepth/2014/may/01/the-drop-heard-round-the-world|access-date=26 July 2014}}</ref>

==National Museum of Scotland experiment==
Another pitch-in-funnel demonstration was begun in 1902 by the [[Royal Scottish Museum]] in [[Edinburgh]] and is in Edinburgh at the Royal Scottish Museum's successor institution the [[National Museum of Scotland]].<ref name="nms_experiment_cat_entry">{{cite web|url=https://www.nms.ac.uk/explore-our-collections/collection-search-results/?item_id=205915|title=Apparatus / fluidity / pitch|website=National Museums Scotland|access-date=May 5, 2023}}</ref> The known records of its behaviour are incomplete: it is known to have dripped once at some time between 4 and 6 June 2016 and on at least one occasion in the past, but the time and number of the previous drip or drips is unknown. Furthermore, the June 2016 drip happened shortly after the experiment was taken out of museum storage, and the physical movement may have caused it to drip at that time.<ref name="nms_experiment_story">{{cite web|url=https://www.nms.ac.uk/explore-our-collections/stories/science-and-technology/made-in-scotland-changing-the-world/scottish-science-innovations/pitch-drop-demonstration/|title=Pitch drop demonstration|website=National Museums Scotland|access-date=May 5, 2023}}</ref>

==Demonstrations of Lord Kelvin==
[[File:Kelvin pitch glacier.JPG|thumb|right|Kelvin's glacier model]]
In the [[Hunterian Museum]] at the [[University of Glasgow]] are two pitch-based demonstrations by [[Lord Kelvin]] from the 19th century. Kelvin placed some bullets on top of a dish of pitch, and [[Cork (material)|cork]]s at the bottom: over time, the bullets sank and the corks floated.

Lord Kelvin also showed that the pitch flows like [[glacier]]s, with a [[mahogany]] ramp that allowed it to slide slowly downward and form shapes and patterns similar to glaciers in the [[Alps]].<ref name="BBC1" /> This model was considered as an inspiration for the expected properties of [[luminiferous aether]].<ref>{{cite journal | doi = 10.1007/s00016-006-0310-6 | title = The Physical Tourist Physics in Glasgow: A Heritage Tour | author = Johnston, S.F. | journal =  Physics in Perspective | volume = 8 | pages=451–465 | year=2006| issue = 4 | bibcode = 2006PhP.....8..451J }}</ref><ref>{{cite book | chapter-url = https://archive.org/details/scientificpapers0030unse/page/276/mode/2up?q=pitch | author = Baron Kelvin of Largs | title = Scientific Papers: physics, chemistry, astronomy, geology, with introductions, notes and illustrations - Volume XXX | year = 1910 | chapter = The Wave Theory of Light}}</ref>

==See also==
{{Portal|Queensland|Ireland|Scotland|Wales|Science}}
* [[Rheology]]
* [[William James Beal]], botanist who started a long-running seed germination experiment in 1879
* [[Oxford Electric Bell]], ringing nearly continuously from 1840
* [[Centennial Light]], light bulb burning since 1901
* The [[E. coli long-term evolution experiment]] (LTEE), a study in [[experimental evolution]] running since 1988.

==References==
{{reflist}}

==External links==
{{commons category}}
* {{cite web |url= http://smp.uq.edu.au/content/pitch-drop-experiment |title= Pitch Drop Experiment |date= 6 January 2016 |publisher= [[University of Queensland]] }}
* {{cite web |url= http://www.thetenthwatch.com/ |title= The Tenth Watch Live Webcam Feed |publisher= [[University of Queensland]] }}
** {{cite web |url= http://www.physics.uq.edu.au/physics_museum/pitch2.gif |title= Picture of the sixth drop shortly after falling in 1979 |url-status= unfit |year= 1979 |archive-date= Sep 17, 2000 |archive-url= https://web.archive.org/web/20000917202556/http://www.physics.uq.edu.au/physics_museum/pitch2.gif }}
* {{cite web |url= https://www.tcd.ie/physics/300/pitch-tar/ |title= Welcome to the National Pitch Drop |publisher= [[Trinity College Dublin]] }}

[[Category:Fluid dynamics]]
[[Category:Physics experiments]]
[[Category:University of Queensland]]
[[Category:1927 introductions]]
[[Category:1927 in science]]
[[Category:Asphalt]]