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Thomas Parnell
The Pitch Drop Experiment
Hands On Activity: My Putty Drop Experiment

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  • The Pitch Drop Experiment

    Thomas Parnell's pitch drop experiment from 1927
    CC 3.0 / GNU 1.2

    The purpose of the Pitch Drop Experiment is to demonstrate that there are materials that even if they look solid at room temperature, like pitch that could be smashed by a hammer blow, they are as a matter of fact high viscosity fluids.

    The meaning is that pitch, for example, can flow, at room temperature, very slowly and form a single drop after a few years.

    To test this assumption there is a need for a long term experiment.

    The experiment was initiated in 1927 by Thomas Parnell (1881 – 1948) who was the first Professor of Physics at the University of Queensland, Brisbane, Australia. Parnell poured melted pitch into a blocked glass funnel and allowed it to settle down for three years. In 1930 the neck of the funnel was unblocked and the pitch started flowing. Drops formed slowly and fell approximately every ten years a drop. Till now fell eight drops and the ninth is expected in 2012 or 2013.

    In 2005, John Mainstone, experiment's current custodian, and Thomas Parnell (died in 1948) were awarded the Ig Nobel Prize in Physics for the pitch drop experiment.

    To date, no one has ever witnessed a drop fall. The experiment is in permanent view of a webcam although technical problems prevented the most recent drop (the 8th) from being recorded.

    The experiment is on public display in the Parnell Building, School of Physics, St Lucia campus, University of Queensland, Australia.

    Experiment Timeline:
    1927 - Experiment set up
    1930 - The funnel stem was unblocked
    1938 - 1st drop fell - 8 years interval
    1947 - 2nd drop fell - 8 years interval
    1954 - 3rd drop fell - 7 years interval
    1962 - 4th drop fell - 8 years interval
    1970 - 5th drop fell - 8 years interval
    1979 - 6th drop fell - 9 years interval
    1988 - 7th drop fell - 9 years interval
    2000 - 8th drop fell - 12 years interval
    Source: Wikipedia

    See also:

    In 1927, the St Andrew's University in Scotland also has started a pitch drop experiment of its own. While the Parnell experiment has produced a series of drops, the pitch at St Andrew's flows out in a continuous dribble maybe because of the difference between the pitch samples. (

    In 1887, Lord Kelvin started his pitch glacier experiment at Glasgow University which is still going. In this experiment a pitch bulk flows very slowly unnoticed down a slide. Kelvin's experiment demonstrated that small consistent forces, such as gravity, are able to produce big changes in the shape of a substance over long periods of time. However, Kelvin's objective was not to demonstrate properties of matter but to illustrate properties of ether (out of scope for this page). (

    Point of Controversy: such experiments and others led some to the view that solids are as a matter of fact liquids with a very high viscosity.

    My Putty Drop Experiment

    My Putty Drop Experiment from May 2012

    For school demonstrations or science fair projects is not practical to wait a decade or so to witness a pitch drop. So we suggest trying other materials that have lower viscosity that will provide results in weeks or months but not years.

    For this experiment we chose sta-put putty (plumbers putty / window putty) that even if it doesn't harden completely it still has a very high viscosity (108 times of that of water but substantial lower than pitch's 2.3×1011) and hopefully it will produce drops in a reasonable time and by that it will demonstrate Parnell's point that sometimes solids (look like) are high viscosity fluids that can flow, but very slowly, and even can form drops like liquids.

    Other possible material is plasteline.

    The funnel was sealed and filled with putty to the brim. The malleable putty was compressed into the funnel, as much as possible, using hands. Now we are going to leave it settle down to eliminate air bubbles if such were created in the compression process. When the level of putty goes down a few millimeters it's time to cut the stem, if not we are going to wait one year before we do it.

    The experiment was set up in 20 May 2012 in Dimona, Israel where the temperature fluctuates most of the time between 10°C (January) to 35 °C (August).

    We are going to use the data collected from this experiment (if successful) to calculate the viscosity of putty and compare the obtained value to more official data.

    We are going to keep our readers updated on new developments on the following experiment log ASAP.

    The Putty Drop Experiment Log

    20 May 2012 - The experiment starts (see above).

    22 May 2013 - The neck of the funnel is cut.

    Links of Interest

    University of Queensland page on the Pitch Drop experiment with live webcam
    Pitch Drop Experiment - Wikipedia
    Is this the most boring experiment ever? Scientists watch drops of pitch form - Mail Online
    A Test of Patience

    My Dog Kelly

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    Last updated: June 2013
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