Post date: Jul 22, 2013 12:8:22 PM
The once-in-a-decade fall of a drop of pitch has been recorded on camera for the first time in Ireland. The experiment, started in 1944 by scientists at Trinity CollegeDublin, is one of the world's longest running.
DUBLIN, IRELAND (RECENT) (TRINITY COLLEGE DUBLIN) - One of the world's longest running experiments, which began nearly 70 years ago at Trinity College Dublin (TCD), has now recorded the fall of a drop of pitch on video for the first time.
A group of physicists at TCD began the experiment in 1944 to test if pitch is solid or liquid. The experiment was established to demonstrate that pitch is a material that flows, albeit with an incredibly high viscosity, hence extremely slowly. Also known as asphalt or bitumen, pitch appears to be solid at room temperature.Pitch drop experiments are long-term versions of a standard experiment used to measure the viscosity of liquids, using a Ford viscosity cup, which contains a funnel-like structure at the bottom. It is normally used to measure the viscosity of paints based on the time required for a test sample to drain out.
Produced along with charcoal from the destructive distillation of pine and other resinous woods, pitch is a polymer for which the viscosity (resistance to force) is sufficiently large that it appears to be a brittle solid. However, if subjected to a stress for a long period of time, it will flow. This makes pitch a good sealant.
Both the Trinity College and a similar experiment started at Australia's University of Queensland in 1927 have resulted in drops of pitch falling free of the viscosity cup, but at the rate of about one drop per decade. The viscosity of pitch is at least 20 billion times the viscosity of water.
Whilst pitch has been dropping from the funnel in Trinity since 1944, nobody had ever previously witnessed a drop fall.
In May of this year, with the latest drop about to fall, Professor Shane Berginbroadcast the experiment via the web. On July 11 the drop dripped. Despite efforts by the Queensland researchers, none of the eight fallen drops have been observed to fall. A ninth is expected to fall later this year, and the apparatus is under continuous video and webcam surveillance.
Tracking the evolution of the drop, Professor Denis Weaire, Professor Stefan Hutzler and David Whyte, all from TCD, calculated the viscosity of the pitch to be 2x107 Pa s, approximately 2 million times the viscosity of honey.