The Pitch Dropped!
Humanity has accomplished a new first!
Published July 19, 2013
Last Thursday, something happened that has never happened before. After almost 70 thwarted years, a simple drip proved that basic scientific curiosity can still yield novel delights, as well as the viscosity of pitch. And, the moment was observed!
Pitch, made from wood, coal, or petroleum, is a viscoelastic polymer. Though apparently solid at room temperature—so much so that it can shatter—it's actually flowing. Very, very slowly. Viscosity describes a fluid's resistance to flow and is determined by the interactions of particles within a system. In liquids, viscosity usually decreases as temperature rises (so the liquid flows more quickly) because the speed of the constituent molecules increases, cutting down the amount of contact between molecules and resultant friction. In gases, this is reversed. At higher temperatures, gas molecules collide more frequently. For a more thorough explanation of the physics involved, click here. Superfluids, which have zero viscosity, seem to defy gravity.
Pitch is well at the other end of the spectrum, with a viscosity 230 billion times that of water. If you heat it, put it into a funnel, and let it cool, it will drip at a rate of about once a decade. This very experiment was set up at the University of Queensland in 1927 and at Trinity College Dublin in 1944. Since then, nobody had managed to observe a single drop. This Radiolab podcast with Professor John Mainstone, long-time custodian of the Queensland experiment, details the tragicomic series of missed drip sightings. At last, on July 18, 2013, scientists at Trinity College—and anyone felicitously watching the webcam at the right moment—participated in a human first and watched the pitch drop!
It's not every day one gets to do something that's never happened before. "It summed up why I like being a scientist," says Trinity College School of Physics Professor Shane Bergin. "It acts as a catalyst for curiosity, and that's, for me, what the driving force of science is."
The Queensland pitch is looking ripe for the dripping as well. Test your luck catching the drop fall live here. "You, yourself," writes Megan Garber for The Atlantic, "can do what nobody had done before: catch the viscous pitch, the unicorn of the scientific world, in the act of dropping."
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