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D - 23: The Unexpected Usefulness of the Tower of Pisa

Updated: Mar 26, 2021

Yesterday, we wondered about the marbles of the Tower of Pisa and where they were from. Today, we are going to talk about what the tower was used for. Built in the 12th century as bell tower to call the citizen to church, the ringing of its bells also signaled the start and end of the workday and alerted people to gather in case of extraordinary events. The beautiful bells from the 13th century are still up in the tower and look perfectly functional. Have only heard the smallest one ring and wonder whether the others are still functionable.

Today, the Leaning Tower has a different purpose. It attracts a much bigger crowd than just the local church goers. Tourists arrive from all over the world, usually for a day, mostly in giant coaches and almost all dressed in T-shirt, shorts and flip-flops. All equipped with their cameras or smart phones. The Tower of Pisa is something that nobody on an Italian holiday wants to miss. The queue for climbing the tower is long and waiting time in the summer heat easily extends beyond an hour. Good business for the sellers of bottled water.

The Bell Platform in the Tower of Pisa

When researching how the tower was built, I discovered a function which I did not expect: the use of it as platform for physics experiment. Legend has it that Galileo Galilei dropped spheres of different size and weight from the bell platform. He was one of the first scientists to systematically research gravity and did it on falling objects. According to Aristoteles heavier objects fell faster than lighter. Galileo Galilei, a young mathematics professor at the University of Pisa from 1589 – 1594, wanted to see whether this was true. What better idea than using the Leaning Tower to find out. Nobody knows whether the story is really true but it is simply too good for not being told. But we know that Galileo was able to prove that the mass of an object does not determine its falling speed. Light and heavy objects fall with the same velocity. We also know that Galileo loved to work from the top of bell towers. He did it again in Venice when he demonstrated the usefulness of his telescope to the Doge – you could detect enemy sails much earlier than by naked eye or when he studied the night sky with it.

During his experiments with the spheres, Galileo noticed that their dropping speed was not constant. It actually accelerated. But by how much? He did not have the instruments to measure their acceleration. Watches able to show seconds were not invented yet. They were another 200 years in the future. But this was not the type of problem which deterred Galileo - it inspired him to try harder. If the spheres were falling too fast to measure, he had to slow them down. He came up with the inclined plane experiment, built a simple plane with a grove, inclined it and rolled his spheres down the grove. What he found revolutionized science and broadened our understanding of gravity. It was a force that accelerated exponentially.

A replica of Galileo's inclined plane - built in the US in 1995

From his early days as mathematics professor in Pisa, Galileo would go on and become one of the preeminent scientists of his time. He moved to Padua, worked for the Arsenal of Venice, built the first usable telescopes for the Venetian Fleet, used one of them on the night sky and detected the moons of Jupiter, became a vocal advocate of a helio-centric universe and run into trouble with the catholic church which eventually put him under house arrest for the rest of his life. “E pur si muove – and yet it moves”. We all know the story

Galileo Galilei painted by Tintoretto

Life is full of lucky coincidences. When Galileo became a professor for mathematics in Pisa in 1589, he was only 25 years old. By that time, the Tower of Pisa had been leaning for almost 300 years. Had he become professor in Florence where there was no such thing, would he have imagined the experiment with the spheres and challenged Aristoteles? We do not know. The rapid advance of guns in warfare made the development of ballistic science an absolute necessity. Probably someone else would have picked up the challenge of defining gravity had Galileo not done it. But the Leaning Tower was there and the honor fell to Galileo. Being at the right place at the right time is always a recipe for success.

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