The Pitch Drop experiment, acknowledged by the Guinness Book of Records as the longest-running scientific experiment globally, is a significant part of the legacy for generations of staff and students at the University of Queensland (UQ).
Professor Thomas Parnell, the first Professor of Physics at the University of Queensland, initiated the Pitch Drop experiment in 1927 to showcase the surprising properties of everyday materials. This experiment highlights the fluidity and high viscosity of pitch, a tar derivative that was historically used for waterproofing boats. While pitch appears solid and brittle at room temperature, capable of shattering with a hammer's strike, it is, in fact, a fluid at that temperature, making the experiment particularly fascinating.
In 1927, Professor Parnell heated a sample of pitch and poured it into a glass funnel with a sealed stem. After allowing three years for the pitch to settle, the sealed stem was cut in 1930. Since then, the pitch has been dripping out of the funnel at an incredibly slow rate, with the tenth drop only now beginning to form after more than 80 years.
The Pitch Drop experiment was initially established as an example and is not maintained under specific environmental conditions; it is displayed in a cabinet in the foyer of the Department. As a result, the pitch's flow rate fluctuates with seasonal temperature changes. However, researchers have estimated the viscosity of this pitch sample, revealing it to be approximately 100 billion times more viscous than water, according to a paper by Edgeworth et al. The late Professor John Mainstone, who co-custodied the experiment with Professor Parnell, was awarded the Ig Nobel Prize for Physics in 2005 for his long-term dedication to the project.
In the over 80 years that the pitch has been dripping, no one has ever witnessed a drop fall. However, a live video feed is now available online, allowing viewers the chance to be among the first to see it happen. The feed also captures students from The University of Queensland moving around outside the cabinet, making it a more engaging experience than simply watching grass grow.
