The pitch drop experiment began in 1927 when Professor Thomas Parnell of the University of Queensland in Brisbane, Australia, set out to demonstrate to his students that some substances that appear to be solid are in fact very high viscous fluids. He used tar pitch, or bitumen, a derivative of coal once used to waterproof boats, in an experiment to prove his point. At room temperature, pitch appears to be solid and can even shatter if hit with a hammer, but despite its look and feel, pitch can also flow, albeit extremely slowly.
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Curious visitors inspecting the setup of the pitch drop experiment. Photo: University of Queensland